diff --git a/.circleci/config.yml b/.circleci/config.yml
index c80a69b5129..34ffbca9d64 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -15,68 +15,57 @@ jobs:
           command: "black --check ."
 
   # Core
-  python-2.7-core:
+  python-3.6-core:
     docker:
-      - image: circleci/python:2.7-stretch-node-browsers
-        environment:
-          PLOTLY_TOX_PYTHON_27: python2.7
+      - image: circleci/python:3.6-stretch-node-browsers
 
     steps:
       - checkout
       - run:
-          name: Install tox
-          command: "sudo pip install tox"
+          name: Install dependencies
+          command: "cd packages/python; sudo pip install -r ./plotly/test_requirements/requirements_36_core.txt"
       - run:
-          name: Test with tox
-          command: "cd packages/python/plotly; tox -e py27-core"
+          name: Test core
+          command: "cd packages/python/plotly; pytest plotly/tests/test_core"
           no_output_timeout: 20m
 
-  python-3.5-core:
+  python-3.7-core:
     docker:
-      - image: circleci/python:3.5-stretch-node-browsers
-        environment:
-          PLOTLY_TOX_PYTHON_35: python3.5
-
+      - image: circleci/python:3.7-stretch-node-browsers
     steps:
       - checkout
       - run:
-          name: Install tox
-          command: "sudo pip install tox"
+          name: Install dependencies
+          command: "cd packages/python; sudo pip install -r ./plotly/test_requirements/requirements_37_core.txt"
       - run:
-          name: Test with tox
-          command: "cd packages/python/plotly; tox -e py35-core"
+          name: Test core
+          command: "cd packages/python/plotly; pytest plotly/tests/test_core"
           no_output_timeout: 20m
 
-  python-3.6-core:
+  python-3.8-core:
     docker:
-      - image: circleci/python:3.6-stretch-node-browsers
-        environment:
-          PLOTLY_TOX_PYTHON_36: python3.6
-
+      - image: circleci/python:3.8-buster-node-browsers
     steps:
       - checkout
       - run:
-          name: Install tox
-          command: "sudo pip install tox"
+          name: Install dependencies
+          command: "cd packages/python; sudo pip install -r ./plotly/test_requirements/requirements_38_core.txt"
       - run:
-          name: Test with tox
-          command: "cd packages/python/plotly; tox -e py36-core"
+          name: Test core
+          command: "cd packages/python/plotly; pytest plotly/tests/test_core"
           no_output_timeout: 20m
 
-  python-3.7-core:
+  python-3.9-core:
     docker:
-      - image: circleci/python:3.7-stretch-node-browsers
-        environment:
-          PLOTLY_TOX_PYTHON_37: python3.7
-
+      - image: circleci/python:3.9-buster-node-browsers
     steps:
       - checkout
       - run:
-          name: Install tox
-          command: "sudo pip install tox"
+          name: Install dependencies
+          command: "cd packages/python; sudo pip install -r ./plotly/test_requirements/requirements_39_core.txt"
       - run:
-          name: Test with tox
-          command: "cd packages/python/plotly; tox -e py37-core"
+          name: Test core
+          command: "cd packages/python/plotly; pytest plotly/tests/test_core"
           no_output_timeout: 20m
 
   python-3.7-percy:
@@ -112,178 +101,130 @@ jobs:
             rm test/percy/*.html
 
   # Optional
-  python-2.7-optional:
+  python-3.6-optional:
     docker:
-      - image: circleci/python:2.7-stretch-node-browsers
-        environment:
-          PLOTLY_TOX_PYTHON_27: python2.7
+      - image: circleci/python:3.6-stretch-node-browsers
 
     steps:
       - checkout
       - run:
-          name: Install tox
-          command: "sudo pip install tox"
+          name: Install dependencies
+          command: "cd packages/python; sudo pip install -r ./plotly/test_requirements/requirements_36_optional.txt"
       - run:
-          name: Test with tox
-          command: "cd packages/python/plotly; tox -e py27-optional"
+          name: Test core
+          command: "cd packages/python/plotly; pytest plotly/tests/test_core"
           no_output_timeout: 20m
-
-  python-3.5-optional:
-    docker:
-      - image: circleci/python:3.5-stretch-node-browsers
-        environment:
-          PLOTLY_TOX_PYTHON_35: python3.5
-
-    steps:
-      - checkout
       - run:
-          name: Install tox
-          command: "sudo pip install tox"
+          name: Test optional
+          command: "cd packages/python/plotly; pytest plotly/tests/test_optional"
+          no_output_timeout: 40m
       - run:
-          name: Test with tox
-          command: "cd packages/python/plotly; tox -e py35-optional"
+          name: Test utils
+          command: "cd packages/python/plotly; pytest _plotly_utils/tests/"
           no_output_timeout: 20m
-
-  python-3.6-optional:
-    docker:
-      - image: circleci/python:3.6-stretch-node-browsers
-        environment:
-          PLOTLY_TOX_PYTHON_36: python3.6
-
-    steps:
-      - checkout
       - run:
-          name: Install tox
-          command: "sudo pip install tox"
-      - run:
-          name: Test with tox
-          command: "cd packages/python/plotly; tox -e py36-optional"
+          name: Test io
+          command: "cd packages/python/plotly; pytest plotly/tests/test_io"
           no_output_timeout: 20m
 
   python-3.7-optional:
     docker:
       - image: circleci/python:3.7-stretch-node-browsers
-        environment:
-          PLOTLY_TOX_PYTHON_37: python3.7
 
     steps:
       - checkout
       - run:
-          name: Install tox
-          command: "sudo pip install tox"
+          name: Install dependencies
+          command: "cd packages/python; sudo pip install -r ./plotly/test_requirements/requirements_37_optional.txt"
       - run:
-          name: Test with tox
-          command: "cd packages/python/plotly; tox -e py37-optional"
+          name: Test core
+          command: "cd packages/python/plotly; pytest plotly/tests/test_core"
           no_output_timeout: 20m
-
-  # Plot.ly
-  python-2.7-plot_ly:
-    docker:
-      - image: circleci/python:2.7-stretch-node-browsers
-        environment:
-          PLOTLY_TOX_PYTHON_27: python2.7
-
-    steps:
-      - checkout
       - run:
-          name: Install tox
-          command: "sudo pip install tox"
+          name: Test optional
+          command: "cd packages/python/plotly; pytest plotly/tests/test_optional"
+          no_output_timeout: 40m
+      - run:
+          name: Test utils
+          command: "cd packages/python/plotly; pytest _plotly_utils/tests/"
+          no_output_timeout: 20m
       - run:
-          name: Test with tox
-          command: "cd packages/python/chart-studio; tox -e py27-plot_ly"
+          name: Test io
+          command: "cd packages/python/plotly; pytest plotly/tests/test_io"
           no_output_timeout: 20m
+      - run:
+          name: Test dependencdies not imported
+          command: "cd packages/python/plotly; pytest -x test_init/test_dependencies_not_imported.py"
+      - run:
+          name: Test lazy imports
+          command: "cd packages/python/plotly; pytest -x test_init/test_lazy_imports.py"
 
-  python-3.5-plot_ly:
+  python-3.8-optional:
     docker:
-      - image: circleci/python:3.5-stretch-node-browsers
-        environment:
-          PLOTLY_TOX_PYTHON_35: python3.5
+      - image: circleci/python:3.8-buster-node-browsers
 
     steps:
       - checkout
       - run:
-          name: Install tox
-          command: "sudo pip install tox"
+          name: Install dependencies
+          command: "cd packages/python; sudo pip install -r ./plotly/test_requirements/requirements_38_optional.txt"
       - run:
-          name: Test with tox
-          command: "cd packages/python/chart-studio; tox -e py35-plot_ly"
+          name: Test core
+          command: "cd packages/python/plotly; pytest plotly/tests/test_core"
           no_output_timeout: 20m
-
-  python-3.7-plot_ly:
-    docker:
-      - image: circleci/python:3.7-stretch-node-browsers
-        environment:
-          PLOTLY_TOX_PYTHON_37: python3.7
-
-    steps:
-      - checkout
       - run:
-          name: Install tox
-          command: "sudo pip install tox"
+          name: Test optional
+          command: "cd packages/python/plotly; pytest plotly/tests/test_optional"
+          no_output_timeout: 40m
+      - run:
+          name: Test utils
+          command: "cd packages/python/plotly; pytest _plotly_utils/tests/"
+          no_output_timeout: 20m
       - run:
-          name: Test with tox
-          command: "cd packages/python/chart-studio; tox -e py37-plot_ly"
+          name: Test io
+          command: "cd packages/python/plotly; pytest plotly/tests/test_io"
           no_output_timeout: 20m
 
-  python-2-7-orca:
+  python-3.9-optional:
     docker:
-      - image: circleci/node:10.9-stretch-browsers
-        environment:
-          PYTHON_VERSION: 2.7
+      - image: circleci/python:3.9-buster-node-browsers
 
     steps:
       - checkout
-      - restore_cache:
-          keys:
-            - conda-27-v1-{{ checksum ".circleci/create_conda_optional_env.sh" }}
       - run:
-          name: Create conda environment
-          command: .circleci/create_conda_optional_env.sh
-
-      - save_cache:
-          key: conda-27-v1-{{ checksum ".circleci/create_conda_optional_env.sh" }}
-          paths:
-            - /home/circleci/miniconda/
+          name: Install dependencies
+          command: "cd packages/python; sudo pip install -r ./plotly/test_requirements/requirements_39_optional.txt"
       - run:
-          name: Run Tests
-          command: |
-            . /home/circleci/miniconda/etc/profile.d/conda.sh
-            conda activate circle_optional
-            pytest --disable-warnings packages/python/plotly/plotly/tests/test_core
-            pytest packages/python/plotly/plotly/tests/test_orca
-
-      - store_artifacts:
-          path: plotly/tests/test_orca/images/linux/failed
+          name: Test core
+          command: "cd packages/python/plotly; pytest plotly/tests/test_core"
+          no_output_timeout: 20m
+      - run:
+          name: Test optional
+          command: "cd packages/python/plotly; pytest plotly/tests/test_optional"
+          no_output_timeout: 40m
+      - run:
+          name: Test utils
+          command: "cd packages/python/plotly; pytest _plotly_utils/tests/"
+          no_output_timeout: 20m
+      - run:
+          name: Test io
+          command: "cd packages/python/plotly; pytest plotly/tests/test_io"
+          no_output_timeout: 20m
 
-  python-3-5-orca:
+  # Chart studio
+  python-3.7-chart_studio:
     docker:
-      - image: circleci/node:10.9-stretch-browsers
-        environment:
-          PYTHON_VERSION: 3.5
+      - image: circleci/python:3.7-stretch-node-browsers
 
     steps:
       - checkout
-      - restore_cache:
-          keys:
-            - conda-35-v1-{{ checksum ".circleci/create_conda_optional_env.sh" }}
       - run:
-          name: Create conda environment
-          command: .circleci/create_conda_optional_env.sh
-
-      - save_cache:
-          key: conda-35-v1-{{ checksum ".circleci/create_conda_optional_env.sh" }}
-          paths:
-            - /home/circleci/miniconda/
+          name: Install dependencies
+          command: "cd packages/python; sudo pip install -r ./chart-studio/test_requirements/requirements_37.txt"
       - run:
-          name: Run Tests
-          command: |
-            . /home/circleci/miniconda/etc/profile.d/conda.sh
-            conda activate circle_optional
-            pytest --disable-warnings packages/python/plotly/plotly/tests/test_core
-            pytest packages/python/plotly/plotly/tests/test_orca
-
-      - store_artifacts:
-          path: plotly/tests/test_orca/images/linux/failed
+          name: Tests
+          command: "cd packages/python/chart-studio; pytest -x chart_studio/tests/"
+          no_output_timeout: 20m
 
   python-3-7-orca:
     docker:
@@ -295,7 +236,7 @@ jobs:
       - checkout
       - restore_cache:
           keys:
-            - conda-37-v1-{{ checksum ".circleci/create_conda_optional_env.sh" }}
+            - conda-37-v1-{{ checksum ".circleci/create_conda_optional_env.sh" }}-{{ checksum "packages/python/plotly/test_requirements/requirements_37_optional.txt" }}
       - run:
           name: Create conda environment
           command: .circleci/create_conda_optional_env.sh
@@ -320,14 +261,13 @@ jobs:
     docker:
       - image: circleci/python:3.7-stretch-node-browsers
         environment:
-          PLOTLY_TOX_PYTHON_37: python3.7
           LANG: en_US.UTF-8
 
     steps:
       - checkout
       - run:
-          name: Install tox
-          command: "sudo pip install tenacity tox black inflect"
+          name: Install dependencies
+          command: "cd packages/python; sudo pip install -r ./plotly/test_requirements/requirements_37_core.txt black inflect"
       - run:
           name: Update jupyterlab-plotly version
           command: "cd packages/python/plotly; python setup.py updateplotlywidgetversion"
@@ -335,11 +275,8 @@ jobs:
           name: Update plotly.js to dev
           command: "cd packages/python/plotly; python setup.py updateplotlyjsdev"
       - run:
-          name: Test with tox
-          command: |
-            cd packages/python/plotly
-            locale
-            tox -e py37-core -- -k 'not nodev'
+          name: Test core
+          command: "cd packages/python/plotly; locale; pytest -k 'not nodev' plotly/tests/test_core"
           no_output_timeout: 20m
       - run:
           name: Commit
@@ -517,16 +454,15 @@ workflows:
 
   build:
     jobs:
-      - python-2.7-core
-      - python-3.5-core
       - python-3.6-core
       - python-3.7-core
+      - python-3.8-core
+      - python-3.9-core
       - python-3.7-percy
-      - python-2.7-optional
-      - python-3.5-optional
       - python-3.6-optional
       - python-3.7-optional
-      - python-3.7-plot_ly
-      - python-2-7-orca
+      - python-3.8-optional
+      - python-3.9-optional
+      - python-3.7-chart_studio
       - python-3-7-orca
       - build-doc
diff --git a/packages/python/chart-studio/test_requirements/requirements_37.txt b/packages/python/chart-studio/test_requirements/requirements_37.txt
new file mode 100644
index 00000000000..b30b19ecb92
--- /dev/null
+++ b/packages/python/chart-studio/test_requirements/requirements_37.txt
@@ -0,0 +1,12 @@
+decorator==4.0.9
+nose==1.3.7
+requests==2.12.4
+six==1.10.0
+pytz==2016.10
+retrying==1.3.3
+pytest==3.5.1
+pandas==0.23.2
+numpy==1.14.3
+ipywidgets==7.2.0
+matplotlib==2.2.3
+--editable=./plotly
diff --git a/packages/python/chart-studio/tox.ini b/packages/python/chart-studio/tox.ini
deleted file mode 100644
index faddb36305f..00000000000
--- a/packages/python/chart-studio/tox.ini
+++ /dev/null
@@ -1,86 +0,0 @@
-; Tox is a testing tool that manages virtualenvs for testing multiple Python
-; environments in a consistent/controlled way.
-
-; SETTING ENVIRONMENT VARIABLES AND TOX TESTING VARIABLES
-;
-; You can limit tox testing to certain environments via the `-e` (envlist)
-; command line option:
-;    tox -e py27-core,py34-core
-; OR, you can just set the `TOXENV` environment variable, which is handy:
-;    TOXENV=py27-core,py34-core
-;
-; Integrating with the virtualenvs in Circle CI is a bit of a pain. For
-; whatever reason the "executable" `python35` (at the time of writing) cannot
-; be activated directly. Instead the circle.yml file specifies the actual
-; binary directly. Because of this, you too have to set the following env
-; variables:
-;    PLOTLY_TOX_PYTHON_27=python2.7
-;    PLOTLY_TOX_PYTHON_34=python3.4
-;    ...
-; These will be specific to your machine and may not look like the ones above.
-; If you're not testing with all the python versions (see TOXENV above),
-; there's no need to install and map other versions.
-
-; PASSING ADDITONAL ARGUMENTS TO TEST COMMANDS
-; The {posargs} is tox-specific and passes in any command line args after `--`.
-; For example, given the testing command in *this* file:
-;   pytest {posargs} -x plotly/tests/test_core
-;
-; The following command:
-;   tox -- -k 'not nodev'
-;
-; Tells tox to call:
-;   pytest -k 'not nodev' -x plotly/tests/test_core
-;
-
-[tox]
-; The py{A,B,C}-{X,Y} generates a matrix of envs:
-;   pyA-X,pyA-Y,pyB-X,pyB-Y,pyC-X,pyC-Y
-envlist = py{27,34,37}-plot_ly
-
-; Note that envs can be targeted by deps using the <target>: dep syntax.
-; Only one dep is allowed per line as of the time of writing. The <target>
-; can be a `-` (hyphen) concatenated string of the environments to target
-; with the given dep.
-
-; These commands are general and will be run for *all* environments.
-[testenv]
-passenv=PLOTLY_TOX_*
-whitelist_externals=
-    mkdir
-deps=
-    coverage==4.3.1
-    decorator==4.0.9
-    mock==2.0.0
-    nose==1.3.7
-    requests==2.12.4
-    six==1.10.0
-    pytz==2016.10
-    retrying==1.3.3
-    pytest==3.5.1
-    backports.tempfile==1.0
-    pandas==0.23.2
-    numpy==1.14.3
-    ipywidgets==7.2.0
-    matplotlib==2.2.3
-    --editable=file:///{toxinidir}/../plotly
-
-
-; Plot.ly environments
-[testenv:py27-plot_ly]
-basepython={env:PLOTLY_TOX_PYTHON_27:}
-commands=
-    python --version
-    pytest {posargs} -x chart_studio/tests/
-
-[testenv:py35-plot_ly]
-basepython={env:PLOTLY_TOX_PYTHON_35:}
-commands=
-    python --version
-    pytest {posargs} -x chart_studio/tests/
-
-[testenv:py37-plot_ly]
-basepython={env:PLOTLY_TOX_PYTHON_37:}
-commands=
-    python --version
-    pytest {posargs} -x chart_studio/tests/
diff --git a/packages/python/plotly/_plotly_utils/optional_imports.py b/packages/python/plotly/_plotly_utils/optional_imports.py
index e76eab95f1c..33bd2d05f57 100644
--- a/packages/python/plotly/_plotly_utils/optional_imports.py
+++ b/packages/python/plotly/_plotly_utils/optional_imports.py
@@ -32,5 +32,5 @@ def get_module(name, should_load=True):
             _not_importable.add(name)
         except Exception as e:
             _not_importable.add(name)
-            msg = "Error importing optional module {}".format(name)
+            msg = f"Error importing optional module {name}"
             logger.exception(msg)
diff --git a/packages/python/plotly/plotly/tests/test_core/test_figure_messages/test_add_traces.py b/packages/python/plotly/plotly/tests/test_core/test_figure_messages/test_add_traces.py
index 63f379bbcd8..77054fcc9de 100644
--- a/packages/python/plotly/plotly/tests/test_core/test_figure_messages/test_add_traces.py
+++ b/packages/python/plotly/plotly/tests/test_core/test_figure_messages/test_add_traces.py
@@ -66,36 +66,6 @@ def test_add_traces(self):
         )
 
 
-class TestAddTracesRowsColsDataTypes(TestCase):
-    def test_add_traces_with_iterable(self):
-        import plotly.express as px
-
-        df = px.data.tips()
-        fig = px.scatter(df, x="total_bill", y="tip", color="day")
-        from plotly.subplots import make_subplots
-
-        fig2 = make_subplots(1, 2)
-        fig2.add_traces(fig.data, rows=[1,] * len(fig.data), cols=[1,] * len(fig.data))
-
-        expected_data_length = 4
-
-        self.assertEqual(expected_data_length, len(fig2.data))
-
-    def test_add_traces_with_integers(self):
-        import plotly.express as px
-
-        df = px.data.tips()
-        fig = px.scatter(df, x="total_bill", y="tip", color="day")
-        from plotly.subplots import make_subplots
-
-        fig2 = make_subplots(1, 2)
-        fig2.add_traces(fig.data, rows=1, cols=2)
-
-        expected_data_length = 4
-
-        self.assertEqual(expected_data_length, len(fig2.data))
-
-
 def test_add_trace_exclude_empty_subplots():
     # Add traces
     fig = make_subplots(2, 2)
diff --git a/packages/python/plotly/plotly/tests/test_core/test_utils/test_utils.py b/packages/python/plotly/plotly/tests/test_core/test_utils/test_utils.py
index 6122f27e7ee..0aff7eb2817 100644
--- a/packages/python/plotly/plotly/tests/test_core/test_utils/test_utils.py
+++ b/packages/python/plotly/plotly/tests/test_core/test_utils/test_utils.py
@@ -2,12 +2,8 @@
 
 from unittest import TestCase
 
-import json as _json
-
 from plotly.utils import PlotlyJSONEncoder, get_by_path, node_generator
-from time import time
-import numpy as np
-import plotly.graph_objects as go
+import json as _json
 
 
 class TestJSONEncoder(TestCase):
@@ -21,38 +17,6 @@ def test_invalid_encode_exception(self):
         with self.assertRaises(TypeError):
             _json.dumps({"a": {1}}, cls=PlotlyJSONEncoder)
 
-    def test_fast_track_finite_arrays(self):
-        # if NaN or Infinity is found in the json dump
-        # of a figure, it is decoded and re-encoded to replace these values
-        # with null. This test checks that NaN and Infinity values are
-        # indeed converted to null, and that the encoding of figures
-        # without inf or nan is faster (because we can avoid decoding
-        # and reencoding).
-        z = np.random.randn(100, 100)
-        x = np.arange(100.0)
-        fig_1 = go.Figure(go.Heatmap(z=z, x=x))
-        t1 = time()
-        json_str_1 = _json.dumps(fig_1, cls=PlotlyJSONEncoder)
-        t2 = time()
-        x[0] = np.nan
-        x[1] = np.inf
-        fig_2 = go.Figure(go.Heatmap(z=z, x=x))
-        t3 = time()
-        json_str_2 = _json.dumps(fig_2, cls=PlotlyJSONEncoder)
-        t4 = time()
-        assert t2 - t1 < t4 - t3
-        assert "null" in json_str_2
-        assert "NaN" not in json_str_2
-        assert "Infinity" not in json_str_2
-        x = np.arange(100.0)
-        fig_3 = go.Figure(go.Heatmap(z=z, x=x))
-        fig_3.update_layout(title_text="Infinity")
-        t5 = time()
-        json_str_3 = _json.dumps(fig_3, cls=PlotlyJSONEncoder)
-        t6 = time()
-        assert t2 - t1 < t6 - t5
-        assert "Infinity" in json_str_3
-
 
 class TestGetByPath(TestCase):
     def test_get_by_path(self):
@@ -86,46 +50,3 @@ def test_node_generator(self):
         ]
         for i, item in enumerate(node_generator(node0)):
             self.assertEqual(item, expected_node_path_tuples[i])
-
-
-class TestNumpyIntegerBaseType(TestCase):
-    def test_numpy_integer_import(self):
-        # should generate a figure with subplots of array and not throw a ValueError
-        import numpy as np
-        import plotly.graph_objects as go
-        from plotly.subplots import make_subplots
-
-        indices_rows = np.array([1], dtype=np.int)
-        indices_cols = np.array([1], dtype=np.int)
-        fig = make_subplots(rows=1, cols=1)
-        fig.add_trace(go.Scatter(y=[1]), row=indices_rows[0], col=indices_cols[0])
-
-        data_path = ("data", 0, "y")
-        value = get_by_path(fig, data_path)
-        expected_value = (1,)
-        self.assertEqual(value, expected_value)
-
-    def test_get_numpy_int_type(self):
-        import numpy as np
-        from _plotly_utils.utils import _get_int_type
-
-        int_type_tuple = _get_int_type()
-        expected_tuple = (int, np.integer)
-
-        self.assertEqual(int_type_tuple, expected_tuple)
-
-
-class TestNoNumpyIntegerBaseType(TestCase):
-    def test_no_numpy_int_type(self):
-        import sys
-        from _plotly_utils.utils import _get_int_type
-        from _plotly_utils.optional_imports import get_module
-
-        np = get_module("numpy", should_load=False)
-        if np:
-            sys.modules.pop("numpy")
-
-        int_type_tuple = _get_int_type()
-        expected_tuple = (int,)
-
-        self.assertEqual(int_type_tuple, expected_tuple)
diff --git a/packages/python/plotly/plotly/tests/test_core/test_px/__init__.py b/packages/python/plotly/plotly/tests/test_optional/test_autoshapes/__init__.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_px/__init__.py
rename to packages/python/plotly/plotly/tests/test_optional/test_autoshapes/__init__.py
diff --git a/packages/python/plotly/plotly/tests/test_core/test_autoshapes/common.py b/packages/python/plotly/plotly/tests/test_optional/test_autoshapes/common.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_autoshapes/common.py
rename to packages/python/plotly/plotly/tests/test_optional/test_autoshapes/common.py
diff --git a/packages/python/plotly/plotly/tests/test_core/test_autoshapes/test_annotated_shapes.py b/packages/python/plotly/plotly/tests/test_optional/test_autoshapes/test_annotated_shapes.py
similarity index 99%
rename from packages/python/plotly/plotly/tests/test_core/test_autoshapes/test_annotated_shapes.py
rename to packages/python/plotly/plotly/tests/test_optional/test_autoshapes/test_annotated_shapes.py
index 9c29282c942..8d7c3806991 100644
--- a/packages/python/plotly/plotly/tests/test_core/test_autoshapes/test_annotated_shapes.py
+++ b/packages/python/plotly/plotly/tests/test_optional/test_autoshapes/test_annotated_shapes.py
@@ -28,7 +28,7 @@
 import sys
 import pytest
 import json
-from common import _cmp_partial_dict, _check_figure_layout_objects
+from .common import _cmp_partial_dict, _check_figure_layout_objects
 
 
 @pytest.fixture
diff --git a/packages/python/plotly/plotly/tests/test_core/test_autoshapes/test_annotated_shapes_annotations.json b/packages/python/plotly/plotly/tests/test_optional/test_autoshapes/test_annotated_shapes_annotations.json
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_autoshapes/test_annotated_shapes_annotations.json
rename to packages/python/plotly/plotly/tests/test_optional/test_autoshapes/test_annotated_shapes_annotations.json
diff --git a/packages/python/plotly/plotly/tests/test_core/test_autoshapes/test_axis_span_shapes.py b/packages/python/plotly/plotly/tests/test_optional/test_autoshapes/test_axis_span_shapes.py
similarity index 99%
rename from packages/python/plotly/plotly/tests/test_core/test_autoshapes/test_axis_span_shapes.py
rename to packages/python/plotly/plotly/tests/test_optional/test_autoshapes/test_axis_span_shapes.py
index 4fef85fe338..12d36cf3c04 100644
--- a/packages/python/plotly/plotly/tests/test_core/test_autoshapes/test_axis_span_shapes.py
+++ b/packages/python/plotly/plotly/tests/test_optional/test_autoshapes/test_axis_span_shapes.py
@@ -3,7 +3,7 @@
 from plotly.basedatatypes import _indexing_combinations
 import plotly.express as px
 import pytest
-from common import _cmp_partial_dict, _check_figure_layout_objects
+from .common import _cmp_partial_dict, _check_figure_layout_objects
 
 
 @pytest.fixture
diff --git a/packages/python/plotly/plotly/tests/test_optional/test_offline/test_offline.py b/packages/python/plotly/plotly/tests/test_optional/test_offline/test_offline.py
index d36934d1eae..a50fa4e7675 100644
--- a/packages/python/plotly/plotly/tests/test_optional/test_offline/test_offline.py
+++ b/packages/python/plotly/plotly/tests/test_optional/test_offline/test_offline.py
@@ -40,6 +40,7 @@ def test_iplot_works_after_you_call_init_notebook_mode(self):
 
         @pytest.mark.matplotlib
         def test_iplot_mpl_works(self):
+            plotly.offline.init_notebook_mode()
             # Generate matplotlib plot for tests
             fig = plt.figure()
 
diff --git a/packages/python/plotly/plotly/tests/test_optional/test_px/__init__.py b/packages/python/plotly/plotly/tests/test_optional/test_px/__init__.py
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/packages/python/plotly/plotly/tests/test_core/test_px/test_colors.py b/packages/python/plotly/plotly/tests/test_optional/test_px/test_colors.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_px/test_colors.py
rename to packages/python/plotly/plotly/tests/test_optional/test_px/test_colors.py
diff --git a/packages/python/plotly/plotly/tests/test_core/test_px/test_facets.py b/packages/python/plotly/plotly/tests/test_optional/test_px/test_facets.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_px/test_facets.py
rename to packages/python/plotly/plotly/tests/test_optional/test_px/test_facets.py
diff --git a/packages/python/plotly/plotly/tests/test_core/test_px/test_imshow.py b/packages/python/plotly/plotly/tests/test_optional/test_px/test_imshow.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_px/test_imshow.py
rename to packages/python/plotly/plotly/tests/test_optional/test_px/test_imshow.py
diff --git a/packages/python/plotly/plotly/tests/test_core/test_px/test_marginals.py b/packages/python/plotly/plotly/tests/test_optional/test_px/test_marginals.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_px/test_marginals.py
rename to packages/python/plotly/plotly/tests/test_optional/test_px/test_marginals.py
diff --git a/packages/python/plotly/plotly/tests/test_core/test_px/test_pandas_backend.py b/packages/python/plotly/plotly/tests/test_optional/test_px/test_pandas_backend.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_px/test_pandas_backend.py
rename to packages/python/plotly/plotly/tests/test_optional/test_px/test_pandas_backend.py
diff --git a/packages/python/plotly/plotly/tests/test_core/test_px/test_px.py b/packages/python/plotly/plotly/tests/test_optional/test_px/test_px.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_px/test_px.py
rename to packages/python/plotly/plotly/tests/test_optional/test_px/test_px.py
diff --git a/packages/python/plotly/plotly/tests/test_core/test_px/test_px_functions.py b/packages/python/plotly/plotly/tests/test_optional/test_px/test_px_functions.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_px/test_px_functions.py
rename to packages/python/plotly/plotly/tests/test_optional/test_px/test_px_functions.py
diff --git a/packages/python/plotly/plotly/tests/test_core/test_px/test_px_hover.py b/packages/python/plotly/plotly/tests/test_optional/test_px/test_px_hover.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_px/test_px_hover.py
rename to packages/python/plotly/plotly/tests/test_optional/test_px/test_px_hover.py
diff --git a/packages/python/plotly/plotly/tests/test_core/test_px/test_px_input.py b/packages/python/plotly/plotly/tests/test_optional/test_px/test_px_input.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_px/test_px_input.py
rename to packages/python/plotly/plotly/tests/test_optional/test_px/test_px_input.py
diff --git a/packages/python/plotly/plotly/tests/test_core/test_px/test_px_wide.py b/packages/python/plotly/plotly/tests/test_optional/test_px/test_px_wide.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_px/test_px_wide.py
rename to packages/python/plotly/plotly/tests/test_optional/test_px/test_px_wide.py
diff --git a/packages/python/plotly/plotly/tests/test_core/test_px/test_trendline.py b/packages/python/plotly/plotly/tests/test_optional/test_px/test_trendline.py
similarity index 100%
rename from packages/python/plotly/plotly/tests/test_core/test_px/test_trendline.py
rename to packages/python/plotly/plotly/tests/test_optional/test_px/test_trendline.py
diff --git a/packages/python/plotly/plotly/tests/test_optional/test_subplots/test_make_subplots.py b/packages/python/plotly/plotly/tests/test_optional/test_subplots/test_make_subplots.py
index 0edcacebd1e..09555497ac3 100644
--- a/packages/python/plotly/plotly/tests/test_optional/test_subplots/test_make_subplots.py
+++ b/packages/python/plotly/plotly/tests/test_optional/test_subplots/test_make_subplots.py
@@ -16,3 +16,33 @@ def test_subplot_titles_numpy_array(self):
             subplot_titles=np.array(["", "Inset"]),
         )
         self.assertEqual(fig, expected)
+
+
+class TestAddTracesRowsColsDataTypes(TestCase):
+    def test_add_traces_with_iterable(self):
+        import plotly.express as px
+
+        df = px.data.tips()
+        fig = px.scatter(df, x="total_bill", y="tip", color="day")
+        from plotly.subplots import make_subplots
+
+        fig2 = make_subplots(1, 2)
+        fig2.add_traces(fig.data, rows=[1,] * len(fig.data), cols=[1,] * len(fig.data))
+
+        expected_data_length = 4
+
+        self.assertEqual(expected_data_length, len(fig2.data))
+
+    def test_add_traces_with_integers(self):
+        import plotly.express as px
+
+        df = px.data.tips()
+        fig = px.scatter(df, x="total_bill", y="tip", color="day")
+        from plotly.subplots import make_subplots
+
+        fig2 = make_subplots(1, 2)
+        fig2.add_traces(fig.data, rows=1, cols=2)
+
+        expected_data_length = 4
+
+        self.assertEqual(expected_data_length, len(fig2.data))
diff --git a/packages/python/plotly/plotly/tests/test_optional/test_utils/test_utils.py b/packages/python/plotly/plotly/tests/test_optional/test_utils/test_utils.py
index 79ce6a7f320..3145c0cb139 100644
--- a/packages/python/plotly/plotly/tests/test_optional/test_utils/test_utils.py
+++ b/packages/python/plotly/plotly/tests/test_optional/test_utils/test_utils.py
@@ -9,6 +9,7 @@
 import decimal
 from datetime import datetime as dt
 from unittest import TestCase
+from time import time
 import pytest
 
 import numpy as np
@@ -20,7 +21,9 @@
 import base64
 
 from plotly import optional_imports, utils
+import plotly.graph_objects as go
 from plotly.graph_objs import Scatter, Scatter3d, Figure, Data
+from plotly.utils import get_by_path
 from PIL import Image
 
 
@@ -358,11 +361,101 @@ def test_pil_image_encoding(self):
         j1 = _json.dumps({"source": img}, cls=utils.PlotlyJSONEncoder)
         assert j1 == '{"source": "%s"}' % expected_uri
 
+    def test_nan_to_null(self):
+        array = [1, float("NaN"), float("Inf"), float("-Inf"), "platypus"]
+        result = _json.dumps(array, cls=utils.PlotlyJSONEncoder)
+        expected_result = '[1, null, null, null, "platypus"]'
+        self.assertEqual(result, expected_result)
+
+    def test_invalid_encode_exception(self):
+        with self.assertRaises(TypeError):
+            _json.dumps({"a": {1}}, cls=utils.PlotlyJSONEncoder)
+
+    def test_fast_track_finite_arrays(self):
+        # if NaN or Infinity is found in the json dump
+        # of a figure, it is decoded and re-encoded to replace these values
+        # with null. This test checks that NaN and Infinity values are
+        # indeed converted to null, and that the encoding of figures
+        # without inf or nan is faster (because we can avoid decoding
+        # and reencoding).
+        z = np.random.randn(100, 100)
+        x = np.arange(100.0)
+        fig_1 = go.Figure(go.Heatmap(z=z, x=x))
+        t1 = time()
+        json_str_1 = _json.dumps(fig_1, cls=utils.PlotlyJSONEncoder)
+        t2 = time()
+        x[0] = np.nan
+        x[1] = np.inf
+        fig_2 = go.Figure(go.Heatmap(z=z, x=x))
+        t3 = time()
+        json_str_2 = _json.dumps(fig_2, cls=utils.PlotlyJSONEncoder)
+        t4 = time()
+        assert t2 - t1 < t4 - t3
+        assert "null" in json_str_2
+        assert "NaN" not in json_str_2
+        assert "Infinity" not in json_str_2
+        x = np.arange(100.0)
+        fig_3 = go.Figure(go.Heatmap(z=z, x=x))
+        fig_3.update_layout(title_text="Infinity")
+        t5 = time()
+        json_str_3 = _json.dumps(fig_3, cls=utils.PlotlyJSONEncoder)
+        t6 = time()
+        assert t2 - t1 < t6 - t5
+        assert "Infinity" in json_str_3
+
+
+class TestNumpyIntegerBaseType(TestCase):
+    def test_numpy_integer_import(self):
+        # should generate a figure with subplots of array and not throw a ValueError
+        import numpy as np
+        import plotly.graph_objects as go
+        from plotly.subplots import make_subplots
+
+        indices_rows = np.array([1], dtype=np.int)
+        indices_cols = np.array([1], dtype=np.int)
+        fig = make_subplots(rows=1, cols=1)
+        fig.add_trace(go.Scatter(y=[1]), row=indices_rows[0], col=indices_cols[0])
+
+        data_path = ("data", 0, "y")
+        value = get_by_path(fig, data_path)
+        expected_value = (1,)
+        self.assertEqual(value, expected_value)
+
+    def test_get_numpy_int_type(self):
+        import numpy as np
+        from _plotly_utils.utils import _get_int_type
+
+        int_type_tuple = _get_int_type()
+        expected_tuple = (int, np.integer)
+
+        self.assertEqual(int_type_tuple, expected_tuple)
+
+
+class TestNoNumpyIntegerBaseType(TestCase):
+    def test_no_numpy_int_type(self):
+        import sys
+        from _plotly_utils.utils import _get_int_type
+        from _plotly_utils.optional_imports import get_module
+
+        np = get_module("numpy", should_load=False)
+        if np:
+            sys.modules.pop("numpy")
+
+        int_type_tuple = _get_int_type()
+        expected_tuple = (int,)
+
+        self.assertEqual(int_type_tuple, expected_tuple)
+
 
 if matplotlylib:
 
     @pytest.mark.matplotlib
     def test_masked_constants_example():
+        try:
+            pd.options.plotting.backend = "matplotlib"
+        except Exception:
+            pass
+
         # example from: https://gist.github.com/tschaume/d123d56bf586276adb98
         data = {
             "esN": [0, 1, 2, 3],
diff --git a/packages/python/plotly/setup.py b/packages/python/plotly/setup.py
index 172eb25d8df..093010f5dff 100644
--- a/packages/python/plotly/setup.py
+++ b/packages/python/plotly/setup.py
@@ -457,16 +457,13 @@ def run(self):
     long_description_content_type="text/markdown",
     classifiers=[
         "Development Status :: 5 - Production/Stable",
-        "Programming Language :: Python :: 2",
-        "Programming Language :: Python :: 2.7",
-        "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.3",
-        "Programming Language :: Python :: 3.4",
-        "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
         "Topic :: Scientific/Engineering :: Visualization",
     ],
+    python_requires=">=3.6",
     license="MIT",
     packages=[
         "plotly",
diff --git a/packages/python/plotly/test_requirements/requirements_36_core.txt b/packages/python/plotly/test_requirements/requirements_36_core.txt
new file mode 100644
index 00000000000..6265e5b540e
--- /dev/null
+++ b/packages/python/plotly/test_requirements/requirements_36_core.txt
@@ -0,0 +1,4 @@
+requests==2.12.4
+six==1.10.0
+tenacity==6.2.0
+pytest==3.5.1
diff --git a/packages/python/plotly/test_requirements/requirements_36_optional.txt b/packages/python/plotly/test_requirements/requirements_36_optional.txt
new file mode 100644
index 00000000000..f86591ca21c
--- /dev/null
+++ b/packages/python/plotly/test_requirements/requirements_36_optional.txt
@@ -0,0 +1,24 @@
+requests==2.12.4
+six==1.10.0
+tenacity==6.2.0
+pandas==0.24.2
+numpy==1.19.5
+xarray==0.10.9
+statsmodels==0.10.2
+pillow==5.2.0
+pytest==3.5.1
+pytz==2016.10
+
+--editable=./plotly-geo
+ipython[all]==5.1.0
+ipywidgets==7.2.0
+ipykernel==4.8.2
+jupyter==1.0.0
+scipy==1.2.3
+shapely==1.7.0
+geopandas==0.3.0
+pyshp==1.2.10
+matplotlib==2.2.3
+scikit-image==0.14.4
+psutil==5.7.0
+kaleido
diff --git a/packages/python/plotly/test_requirements/requirements_37_core.txt b/packages/python/plotly/test_requirements/requirements_37_core.txt
new file mode 100644
index 00000000000..6265e5b540e
--- /dev/null
+++ b/packages/python/plotly/test_requirements/requirements_37_core.txt
@@ -0,0 +1,4 @@
+requests==2.12.4
+six==1.10.0
+tenacity==6.2.0
+pytest==3.5.1
diff --git a/packages/python/plotly/test_requirements/requirements_37_optional.txt b/packages/python/plotly/test_requirements/requirements_37_optional.txt
new file mode 100644
index 00000000000..f86591ca21c
--- /dev/null
+++ b/packages/python/plotly/test_requirements/requirements_37_optional.txt
@@ -0,0 +1,24 @@
+requests==2.12.4
+six==1.10.0
+tenacity==6.2.0
+pandas==0.24.2
+numpy==1.19.5
+xarray==0.10.9
+statsmodels==0.10.2
+pillow==5.2.0
+pytest==3.5.1
+pytz==2016.10
+
+--editable=./plotly-geo
+ipython[all]==5.1.0
+ipywidgets==7.2.0
+ipykernel==4.8.2
+jupyter==1.0.0
+scipy==1.2.3
+shapely==1.7.0
+geopandas==0.3.0
+pyshp==1.2.10
+matplotlib==2.2.3
+scikit-image==0.14.4
+psutil==5.7.0
+kaleido
diff --git a/packages/python/plotly/test_requirements/requirements_38_core.txt b/packages/python/plotly/test_requirements/requirements_38_core.txt
new file mode 100644
index 00000000000..7f8c791a85e
--- /dev/null
+++ b/packages/python/plotly/test_requirements/requirements_38_core.txt
@@ -0,0 +1,4 @@
+requests==2.25.1
+six==1.15.0
+tenacity==6.2.0
+pytest==6.2.3
diff --git a/packages/python/plotly/test_requirements/requirements_38_optional.txt b/packages/python/plotly/test_requirements/requirements_38_optional.txt
new file mode 100644
index 00000000000..091c415b25b
--- /dev/null
+++ b/packages/python/plotly/test_requirements/requirements_38_optional.txt
@@ -0,0 +1,24 @@
+requests==2.25.1
+six==1.15.0
+tenacity==6.2.0
+pandas==1.2.4
+numpy==1.20.2
+xarray==0.17.0
+statsmodels
+Pillow==8.2.0
+pytest==6.2.3
+pytz==2021.1
+
+--editable=./plotly-geo
+ipython[all]==7.22.0
+ipywidgets==7.6.3
+ipykernel==5.5.3
+jupyter==1.0.0
+scipy==1.6.2
+Shapely==1.7.1
+geopandas==0.9.0
+pyshp==2.1.3
+matplotlib==2.2.3
+scikit-image==0.18.1
+psutil==5.7.0
+kaleido
diff --git a/packages/python/plotly/test_requirements/requirements_39_core.txt b/packages/python/plotly/test_requirements/requirements_39_core.txt
new file mode 100644
index 00000000000..7f8c791a85e
--- /dev/null
+++ b/packages/python/plotly/test_requirements/requirements_39_core.txt
@@ -0,0 +1,4 @@
+requests==2.25.1
+six==1.15.0
+tenacity==6.2.0
+pytest==6.2.3
diff --git a/packages/python/plotly/test_requirements/requirements_39_optional.txt b/packages/python/plotly/test_requirements/requirements_39_optional.txt
new file mode 100644
index 00000000000..091c415b25b
--- /dev/null
+++ b/packages/python/plotly/test_requirements/requirements_39_optional.txt
@@ -0,0 +1,24 @@
+requests==2.25.1
+six==1.15.0
+tenacity==6.2.0
+pandas==1.2.4
+numpy==1.20.2
+xarray==0.17.0
+statsmodels
+Pillow==8.2.0
+pytest==6.2.3
+pytz==2021.1
+
+--editable=./plotly-geo
+ipython[all]==7.22.0
+ipywidgets==7.6.3
+ipykernel==5.5.3
+jupyter==1.0.0
+scipy==1.6.2
+Shapely==1.7.1
+geopandas==0.9.0
+pyshp==2.1.3
+matplotlib==2.2.3
+scikit-image==0.18.1
+psutil==5.7.0
+kaleido
diff --git a/packages/python/plotly/tox.ini b/packages/python/plotly/tox.ini
deleted file mode 100644
index d4e6254866d..00000000000
--- a/packages/python/plotly/tox.ini
+++ /dev/null
@@ -1,151 +0,0 @@
-; Tox is a testing tool that manages virtualenvs for testing multiple Python
-; environments in a consistent/controlled way.
-
-; SETTING ENVIRONMENT VARIABLES AND TOX TESTING VARIABLES
-;
-; You can limit tox testing to certain environments via the `-e` (envlist)
-; command line option:
-;    tox -e py27-core,py34-core
-; OR, you can just set the `TOXENV` environment variable, which is handy:
-;    TOXENV=py27-core,py34-core
-;
-; Integrating with the virtualenvs in Circle CI is a bit of a pain. For
-; whatever reason the "executable" `python35` (at the time of writing) cannot
-; be activated directly. Instead the circle.yml file specifies the actual
-; binary directly. Because of this, you too have to set the following env
-; variables:
-;    PLOTLY_TOX_PYTHON_27=python2.7
-;    PLOTLY_TOX_PYTHON_34=python3.4
-;    ...
-; These will be specific to your machine and may not look like the ones above.
-; If you're not testing with all the python versions (see TOXENV above),
-; there's no need to install and map other versions.
-
-; PASSING ADDITONAL ARGUMENTS TO TEST COMMANDS
-; The {posargs} is tox-specific and passes in any command line args after `--`.
-; For example, given the testing command in *this* file:
-;   pytest {posargs} plotly/tests/test_core
-;
-; The following command:
-;   tox -- -k 'not nodev'
-;
-; Tells tox to call:
-;   pytest -k 'not nodev' plotly/tests/test_core
-;
-
-[tox]
-; The py{A,B,C}-{X,Y} generates a matrix of envs:
-;   pyA-X,pyA-Y,pyB-X,pyB-Y,pyC-X,pyC-Y
-envlist = py{27,34,35,36,37}-{core,optional},py{27,34,37}
-
-; Note that envs can be targeted by deps using the <target>: dep syntax.
-; Only one dep is allowed per line as of the time of writing. The <target>
-; can be a `-` (hyphen) concatenated string of the environments to target
-; with the given dep.
-
-; These commands are general and will be run for *all* environments.
-[testenv]
-passenv=PLOTLY_TOX_*
-whitelist_externals=
-    mkdir
-deps=
-    coverage==4.3.1
-    decorator==4.0.9
-    mock==2.0.0
-    requests==2.12.4
-    six==1.10.0
-    pytz==2016.10
-    tenacity==6.2.0
-    pytest==3.5.1
-    pandas==0.24.2
-    numpy==1.19.5
-    xarray==0.10.9
-    statsmodels==0.10.2
-    pillow==5.2.0
-    backports.tempfile==1.0
-    optional: --editable=file:///{toxinidir}/../plotly-geo
-    optional: ipython[all]==5.1.0
-    optional: ipywidgets==7.2.0
-    optional: ipykernel==4.8.2
-    optional: jupyter==1.0.0
-    optional: scipy==1.2.3
-    optional: shapely==1.7.0
-    optional: geopandas==0.3.0
-    optional: pyshp==1.2.10
-    optional: matplotlib==2.2.3
-    optional: scikit-image==0.14.4
-    optional: kaleido
-
-; CORE ENVIRONMENTS
-[testenv:py27-core]
-basepython={env:PLOTLY_TOX_PYTHON_27:}
-commands=
-    python --version
-    pytest {posargs} plotly/tests/test_core
-
-[testenv:py35-core]
-basepython={env:PLOTLY_TOX_PYTHON_35:}
-commands=
-    python --version
-    pytest {posargs} plotly/tests/test_core
-
-[testenv:py36-core]
-basepython={env:PLOTLY_TOX_PYTHON_36:}
-commands=
-    python --version
-    pytest {posargs} plotly/tests/test_core
-
-[testenv:py37-core]
-basepython={env:PLOTLY_TOX_PYTHON_37:}
-commands=
-    python --version
-    pytest {posargs} plotly/tests/test_core
-    pytest {posargs} -x test_init/test_dependencies_not_imported.py
-    pytest {posargs} -x test_init/test_lazy_imports.py
-
-; OPTIONAL ENVIRONMENTS
-;[testenv:py27-optional]
-;basepython={env:PLOTLY_TOX_PYTHON_27:}
-;commands=
-;    python --version
-;;   Do some coverage reporting. No need to do this for all environments.
-;    mkdir -p {envbindir}/../../coverage-reports/{envname}
-;    coverage erase
-;    coverage run --include="*/plotly/*" --omit="*/tests*" {envbindir}/nosetests {posargs} plotly/tests
-;    coverage html -d "{envbindir}/../../coverage-reports/{envname}" --title={envname}
-
-[testenv:py27-optional]
-basepython={env:PLOTLY_TOX_PYTHON_27:}
-commands=
-    python --version
-    pytest {posargs} plotly/tests/test_core
-    pytest {posargs} plotly/tests/test_optional
-    pytest _plotly_utils/tests/
-    pytest plotly/tests/test_io
-
-[testenv:py35-optional]
-basepython={env:PLOTLY_TOX_PYTHON_35:}
-commands=
-    python --version
-    pytest {posargs} plotly/tests/test_core
-    pytest {posargs} plotly/tests/test_optional
-    pytest _plotly_utils/tests/
-    pytest plotly/tests/test_io
-
-[testenv:py36-optional]
-basepython={env:PLOTLY_TOX_PYTHON_36:}
-commands=
-    python --version
-    pytest {posargs} plotly/tests/test_core
-    pytest {posargs} plotly/tests/test_optional
-    pytest _plotly_utils/tests/
-    pytest plotly/tests/test_io
-
-[testenv:py37-optional]
-basepython={env:PLOTLY_TOX_PYTHON_37:}
-commands=
-    python --version
-    pytest {posargs} plotly/tests/test_core
-    pytest {posargs} plotly/tests/test_optional
-    pytest _plotly_utils/tests/
-    pytest plotly/tests/test_io