Testing improvements. (#2036)

* Add start_timeout to threaded test server, set to 3 seconds, log thread exceptions.

* noise

* noise

* noise

* Add type annotations to dash testing fixtures.

* Update changelog.

* noise

Author: T4rk1n

Diff for: CHANGELOG.md

@@ -18,6 +18,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 - [#2034](https://github.com/plotly/dash/pull/2034) Add `link_target` prop to dcc.Markdown component. Closes [#1827](https://github.com/plotly/dash/issues/1827)
 
+- [#2035](https://github.com/plotly/dash/pull/2036) Add type annotations to testing fixtures.
+
 ### Fixed
 
 - [#2029](https://github.com/plotly/dash/pull/2029) Restrict the number of props listed explicitly in generated component constructors - default is 250. This prevents exceeding the Python 3.6 limit of 255 arguments. The omitted props are still in the docstring and can still be provided the same as before, they just won't appear in the signature so autocompletion may be affected.
@@ -30,6 +32,10 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 - [#2035](https://github.com/plotly/dash/pull/2035) Fix [#2033](https://github.com/plotly/dash/issues/2033) In-App error reporting does not render HTML.
 
+- [#1970](https://github.com/plotly/dash/pull/1970) dcc.Dropdown Refactor fixes:
+  - Fix bug [#1868](https://github.com/plotly/dash/issues/1868) value does not update when selected option removed from options.
+  - Fix bug [#1908](https://github.com/plotly/dash/issues/1908) Selected options not showing when the value contains a comma.
+
 ### Changed
 
 - [#2016](https://github.com/plotly/dash/pull/2016) Drop the 375px width from default percy_snapshot calls, keep only 1280px
@@ -46,11 +52,6 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   - Upgrade `black` to v22.3.0 for Python 3.7+ - if you use `dash[ci]` and you call `black`, this may alter your code formatting slightly, including more consistently breaking Python 2 compatibility.
   - Many other mainly JS dependency upgrades to the internals of Dash renderer and components. These may patch bugs or improve performance.
 
-### Fixed
-
-- [#1970](https://github.com/plotly/dash/pull/1970) dcc.Dropdown Refactor fixes:
-  - Fix bug [#1868](https://github.com/plotly/dash/issues/1868) value does not update when selected option removed from options.
-  - Fix bug [#1908](https://github.com/plotly/dash/issues/1908) Selected options not showing when the value contains a comma.
 
 ## [2.3.1] - 2022-03-29
 

Diff for: dash/testing/application_runners.py

@@ -142,18 +142,20 @@ def __init__(self, keep_open=False, stop_timeout=3):
         super().__init__(keep_open=keep_open, stop_timeout=stop_timeout)
         self.thread = None
 
+    def running_and_accessible(self, url):
+        if self.thread.is_alive():
+            return self.accessible(url)
+        raise DashAppLoadingError("Thread is not alive.")
+
     # pylint: disable=arguments-differ
-    def start(self, app, **kwargs):
+    def start(self, app, start_timeout=3, **kwargs):
         """Start the app server in threading flavor."""
 
         def _handle_error():
             self.stop()
 
         app.server.errorhandler(500)(_handle_error)
 
-        if self.thread and self.thread.is_alive():
-            self.stop()
-
         def run():
             app.scripts.config.serve_locally = True
             app.css.config.serve_locally = True
@@ -170,16 +172,24 @@ def run():
                 app.run(threaded=True, **options)
             except SystemExit:
                 logger.info("Server stopped")
+            except Exception as error:
+                logger.exception(error)
+                raise error
 
         retries = 0
 
         while not self.started and retries < 3:
             try:
+                if self.thread and self.thread.is_alive():
+                    self.stop()
+
                 self.thread = KillerThread(target=run)
                 self.thread.daemon = True
                 self.thread.start()
                 # wait until server is able to answer http request
-                wait.until(lambda: self.accessible(self.url), timeout=2)
+                wait.until(
+                    lambda: self.running_and_accessible(self.url), timeout=start_timeout
+                )
                 self.started = self.thread.is_alive()
             except Exception as err:  # pylint: disable=broad-except
                 logger.exception(err)

Diff for: dash/testing/plugin.py

@@ -95,33 +95,33 @@ def pytest_runtest_makereport(item, call):  # pylint: disable=unused-argument
 
 
 @pytest.fixture
-def dash_thread_server():
+def dash_thread_server() -> ThreadedRunner:
     """Start a local dash server in a new thread."""
     with ThreadedRunner() as starter:
         yield starter
 
 
 @pytest.fixture
-def dash_process_server():
+def dash_process_server() -> ProcessRunner:
     """Start a Dash server with subprocess.Popen and waitress-serve."""
     with ProcessRunner() as starter:
         yield starter
 
 
 @pytest.fixture
-def dashr_server():
+def dashr_server() -> RRunner:
     with RRunner() as starter:
         yield starter
 
 
 @pytest.fixture
-def dashjl_server():
+def dashjl_server() -> JuliaRunner:
     with JuliaRunner() as starter:
         yield starter
 
 
 @pytest.fixture
-def dash_br(request, tmpdir):
+def dash_br(request, tmpdir) -> Browser:
     with Browser(
         browser=request.config.getoption("webdriver"),
         remote=request.config.getoption("remote"),
@@ -137,7 +137,7 @@ def dash_br(request, tmpdir):
 
 
 @pytest.fixture
-def dash_duo(request, dash_thread_server, tmpdir):
+def dash_duo(request, dash_thread_server, tmpdir) -> DashComposite:
     with DashComposite(
         dash_thread_server,
         browser=request.config.getoption("webdriver"),
@@ -154,7 +154,7 @@ def dash_duo(request, dash_thread_server, tmpdir):
 
 
 @pytest.fixture
-def dashr(request, dashr_server, tmpdir):
+def dashr(request, dashr_server, tmpdir) -> DashRComposite:
     with DashRComposite(
         dashr_server,
         browser=request.config.getoption("webdriver"),
@@ -171,7 +171,7 @@ def dashr(request, dashr_server, tmpdir):
 
 
 @pytest.fixture
-def dashjl(request, dashjl_server, tmpdir):
+def dashjl(request, dashjl_server, tmpdir) -> DashJuliaComposite:
     with DashJuliaComposite(
         dashjl_server,
         browser=request.config.getoption("webdriver"),