Display node ids and the warnings generated by it

The rationale of using node ids is that users can copy/paste it to run a chosen test

testing/test_warnings.py

@@ -4,27 +4,48 @@ import pytest
 WARNINGS_SUMMARY_HEADER = 'warnings summary'
 
 @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 pyfile_with_warnings(testdir, request):
+    """
+    Create a test file which calls a function in a module which generates warnings.
+    """
+    testdir.syspathinsert()
+    test_name = request.function.__name__
+    module_name = test_name.lstrip('test_') + '_module'
+    testdir.makepyfile(**{
+        module_name: '''
+            import warnings
+            def foo():
+                warnings.warn(PendingDeprecationWarning("functionality is pending deprecation"))
+                warnings.warn(DeprecationWarning("functionality is deprecated"))
+                return 1
+        ''',
+        test_name: '''
+            import {module_name}
+            def test_func():
+                assert {module_name}.foo() == 1
+        '''.format(module_name=module_name)
+    })
 
 
 def test_normal_flow(testdir, pyfile_with_warnings):
+    """
+    Check that the warnings section is displayed, containing test node ids followed by
+    all warnings generated by that test node.
+    """
     result = testdir.runpytest()
     result.stdout.fnmatch_lines([
         '*== %s ==*' % WARNINGS_SUMMARY_HEADER,
 
-        '*test_normal_flow.py:3: PendingDeprecationWarning: functionality is pending deprecation',
+        '*test_normal_flow.py::test_func',
+
+        '*normal_flow_module.py:3: PendingDeprecationWarning: functionality is pending deprecation',
         '  warnings.warn(PendingDeprecationWarning("functionality is pending deprecation"))',
 
-        '*test_normal_flow.py:4: DeprecationWarning: functionality is deprecated',
+        '*normal_flow_module.py:4: DeprecationWarning: functionality is deprecated',
         '  warnings.warn(DeprecationWarning("functionality is deprecated"))',
         '* 1 passed, 2 warnings*',
     ])
+    assert result.stdout.str().count('test_normal_flow.py::test_func') == 1
 
 
 def test_setup_teardown_warnings(testdir, pyfile_with_warnings):
@@ -66,7 +87,7 @@ def test_as_errors(testdir, pyfile_with_warnings, method):
     result = testdir.runpytest(*args)
     result.stdout.fnmatch_lines([
         'E       PendingDeprecationWarning: functionality is pending deprecation',
-        'test_as_errors.py:3: PendingDeprecationWarning',
+        'as_errors_module.py:3: PendingDeprecationWarning',
         '* 1 failed in *',
     ])