Add tests and integrated the original code into the core

_pytest/config.py

@@ -74,7 +74,7 @@ default_plugins = (
      "mark main terminal runner python fixtures debugging unittest capture skipping "
      "tmpdir monkeypatch recwarn pastebin helpconfig nose assertion "
      "junitxml resultlog doctest cacheprovider freeze_support "
-     "setuponly setupplan").split()
+     "setuponly setupplan warnings").split()
 
 builtin_plugins = set(default_plugins)
 builtin_plugins.add("pytester")

testing/test_warnings.py

@@ -0,0 +1,60 @@
+import pytest
+
+
+@pytest.fixture
+def pyfile_with_warnings(testdir):
+    testdir.makepyfile('''
+        import warnings
+        def test_func():
+            warnings.warn(PendingDeprecationWarning("functionality is pending deprecation"))
+            warnings.warn(DeprecationWarning("functionality is deprecated"))
+    ''')
+
+
+def test_normal_flow(testdir, pyfile_with_warnings):
+    result = testdir.runpytest_subprocess()
+    result.stdout.fnmatch_lines([
+        '*== pytest-warning summary ==*',
+
+        'WW0 in *test_normal_flow.py:1 the following warning was recorded:',
+        ' test_normal_flow.py:3: PendingDeprecationWarning: functionality is pending deprecation',
+        '  warnings.warn(PendingDeprecationWarning("functionality is pending deprecation"))',
+
+        'WW0 in *test_normal_flow.py:1 the following warning was recorded:',
+        ' test_normal_flow.py:4: DeprecationWarning: functionality is deprecated',
+        '  warnings.warn(DeprecationWarning("functionality is deprecated"))',
+        '* 1 passed, 2 pytest-warnings*',
+    ])
+
+
+@pytest.mark.parametrize('method', ['cmdline', 'ini'])
+def test_as_errors(testdir, pyfile_with_warnings, method):
+    args = ('-W', 'error') if method == 'cmdline' else ()
+    if method == 'ini':
+        testdir.makeini('''
+            [pytest]
+            filterwarnings= error
+            ''')
+    result = testdir.runpytest_subprocess(*args)
+    result.stdout.fnmatch_lines([
+        'E       PendingDeprecationWarning: functionality is pending deprecation',
+        'test_as_errors.py:3: PendingDeprecationWarning',
+        '* 1 failed in *',
+    ])
+
+
+@pytest.mark.parametrize('method', ['cmdline', 'ini'])
+def test_ignore(testdir, pyfile_with_warnings, method):
+    args = ('-W', 'ignore') if method == 'cmdline' else ()
+    if method == 'ini':
+        testdir.makeini('''
+        [pytest]
+        filterwarnings= ignore
+        ''')
+
+    result = testdir.runpytest_subprocess(*args)
+    result.stdout.fnmatch_lines([
+        '* 1 passed in *',
+    ])
+    assert 'pytest-warning summary' not in result.stdout.str()
+