moved content of if block to method. Added unit_test for method. Fixed news to be in imperative tone.

Author: Patrik Kopkan

news/6340.feature

@@ -1,4 +1,4 @@
-Added a new option ``--save-wheel-names`` to command ``wheel``.
+Add a new option ``--save-wheel-names`` to command ``wheel``.
 The option takes a path and creates a file in which
 the filenames of built or downloaded wheels will be stored,
 separated by newlines

src/pip/_internal/commands/wheel.py

@@ -114,6 +114,22 @@ def __init__(self, *args, **kw):
         self.parser.insert_option_group(0, index_opts)
         self.parser.insert_option_group(0, cmd_opts)
 
+    def save_wheelnames(self, requirement_set, wb):
+        entries_to_save = wb.wheel_filenames[::]
+        for req in requirement_set.requirements.values():
+            if req.link.filename.endswith('whl'):
+                entries_to_save.append(req.link.filename)
+        try:
+            with open(wb.path_to_wheelnames, 'w') as file:
+                file.write(
+                    os.linesep.join(
+                        entries_to_save
+                    ) + os.linesep
+                )
+        except EnvironmentError as e:
+            logger.error('Cannot write to the given path: %s%s PermissionError: %s' %
+                         (wb.path_to_wheelnames, os.linesep, str(e)))
+
     def run(self, options, args):
         cmdoptions.check_install_build_global(options)
 
@@ -188,21 +204,7 @@ def run(self, options, args):
                             "Failed to build one or more wheels"
                         )
                     if wb.path_to_wheelnames is not None:
-                        entries_to_save = wb.wheel_filenames[::]
-                        for req in requirement_set.requirements.values():
-                            if req.link.filename.endswith('whl'):
-                                entries_to_save.append(req.link.filename)
-                        try:
-                            with open(wb.path_to_wheelnames, 'w') as file:
-                                file.write(
-                                    '\n'.join(
-                                        entries_to_save
-                                    ) + '\n'
-                                )
-                        except EnvironmentError as e:
-                            logger.error('Cannot write to the given path: %s',
-                                         wb.path_to_wheelnames)
-                            logger.error('PermissionError: %s', str(e))
+                        self.save_wheelnames(requirement_set, wb)
 
                 except PreviousBuildDirError:
                     options.no_clean = True

tests/unit/test_wheel.py

@@ -5,7 +5,7 @@
 import textwrap
 
 import pytest
-from mock import Mock, patch
+from mock import Mock, patch, mock_open
 from pip._vendor.packaging.requirements import Requirement
 
 from pip._internal import pep425tags, wheel
@@ -17,6 +17,7 @@
 from pip._internal.utils.misc import unpack_file
 from tests.lib import DATA_DIR, assert_paths_equal
 
+from pip._internal.commands.wheel import WheelCommand
 
 @pytest.mark.parametrize(
     "s, expected",
@@ -806,3 +807,36 @@ def test_missing_PATH_env_treated_as_empty_PATH_env(self):
             retval_empty = wheel.message_about_scripts_not_on_PATH(scripts)
 
         assert retval_missing == retval_empty
+
+class TestWheelCommand(object):
+    @patch('pip._internal.wheel.WheelBuilder')
+    @patch('pip._internal.commands.wheel.RequirementSet')
+    def test_save_wheelnames(self, mocked_rs, mocked_wb):
+
+        # simulating needed behaviour
+        class Link:
+            def __init__(self, filename):
+                self.filename = filename
+
+        mocked_wb = mocked_wb()
+        mocked_wb.wheel_filenames = ['Flask-1.1.dev0-py2.py3-none-any.whl']
+
+        filenames = [
+            'flask',
+            'Werkzeug-0.15.4-py2.py3-none-any.whl',
+            'Jinja2-2.10.1-py2.py3-none-any.whl',
+            'itsdangerous-1.1.0-py2.py3-none-any.whl',
+            'Click-7.0-py2.py3-none-any.whl'
+        ]
+        List = []
+        expected = mocked_wb.wheel_filenames + filenames[1:]
+        for filename in filenames:
+            install_reg = InstallRequirement(None, None)
+            install_reg.link = Link(filename)
+            List.append(install_reg)
+        mocked_rs.requirements.values = lambda: List
+        m = (mock_open())()
+        with patch('pip._internal.commands.wheel.open', m, create=True):
+            WheelCommand().save_wheelnames(mocked_rs, mocked_wb)
+            handle = m()
+        handle.__enter__().write.assert_called_once_with(os.linesep.join(expected) + os.linesep)