Extract test dependencies from [options.extras_require]test (#61)

It's becoming an increasingly common pattern to declare test
dependencies using [options.extras_require]test. This change merges the
test dependencies declared using that mechanism with any discovered
using [options]test_requires.

colcon_python_setup_py/package_augmentation/python_setup_py.py

@@ -37,14 +37,22 @@ def augment_package(  # noqa: D102
 
         config = get_setup_information(setup_py)
 
-        for dependency_type, option_name in [
+        mapping = {
             ('build', 'setup_requires'),
             ('run', 'install_requires'),
-            ('test', 'tests_require')
-        ]:
-            desc.dependencies[dependency_type] = {
-                create_dependency_descriptor(d)
-                for d in config.get(option_name) or ()}
+            ('test', 'tests_require'),
+        }
+        _map_dependencies(config, mapping, desc.dependencies)
+
+        extras_mapping = {
+            ('test', 'test'),
+            ('test', 'tests'),
+            ('test', 'testing'),
+        }
+        _map_dependencies(
+            config.get('extras_require') or {},
+            extras_mapping,
+            desc.dependencies)
 
         def getter(env):
             nonlocal setup_py
@@ -53,3 +61,11 @@ def getter(env):
         desc.metadata['get_python_setup_options'] = getter
 
         desc.metadata['version'] = config['metadata'].get('version')
+
+
+def _map_dependencies(options, mapping, dependencies):
+    for dependency_type, option_name in mapping:
+        dependencies.setdefault(dependency_type, set())
+        dependencies[dependency_type].update(
+           create_dependency_descriptor(d)
+           for d in options.get(option_name) or ())

test/test_package_identification_python_setup_py.py

@@ -73,6 +73,12 @@ def test_identify():
             "    'runB',\n"
             '  ],\n'
             '  zip_safe=False,\n'
+            '  extras_require={\n'
+            "    'test': ['test2 == 3.0.0'],\n"
+            "    'tests': ['test3'],\n"
+            "    'testing': ['test4'],\n"
+            "    'other': ['not-test'],\n"
+            '  },\n'
             ')\n')
         _setup_information_cache.clear()
         assert extension.identify(desc) is None
@@ -87,3 +93,4 @@ def test_identify():
         assert desc.dependencies['run'] == {'runA', 'runB'}
         dep = next(x for x in desc.dependencies['run'] if x == 'runA')
         assert dep.metadata['version_gt'] == '1.2.3'
+        assert desc.dependencies['test'] == {'test2', 'test3', 'test4'}