Write help and trace messages to stderr (google#54)

* Change test helper `assertOutputMatches` to track stdout and stderr + adds `assertRaisesRegex`
* Write help text to stderr
* Add some test cases for output matching

fire/core.py

@@ -122,26 +122,33 @@ def Fire(component=None, command=None, name=None):
       if help_flag in component_trace.elements[-1].args:
         command = '{cmd} -- --help'.format(cmd=component_trace.GetCommand())
         print(('WARNING: The proper way to show help is {cmd}.\n'
-               'Showing help anyway.\n').format(cmd=pipes.quote(command)))
+               'Showing help anyway.\n').format(cmd=pipes.quote(command)),
+              file=sys.stderr)
 
-    print('Fire trace:\n{trace}\n'.format(trace=component_trace))
+    print('Fire trace:\n{trace}\n'.format(trace=component_trace),
+          file=sys.stderr)
     result = component_trace.GetResult()
     print(
-        helputils.HelpString(result, component_trace, component_trace.verbose))
+        helputils.HelpString(result, component_trace, component_trace.verbose),
+        file=sys.stderr)
     raise FireExit(2, component_trace)
   elif component_trace.show_trace and component_trace.show_help:
-    print('Fire trace:\n{trace}\n'.format(trace=component_trace))
+    print('Fire trace:\n{trace}\n'.format(trace=component_trace),
+          file=sys.stderr)
     result = component_trace.GetResult()
     print(
-        helputils.HelpString(result, component_trace, component_trace.verbose))
+        helputils.HelpString(result, component_trace, component_trace.verbose),
+        file=sys.stderr)
     raise FireExit(0, component_trace)
   elif component_trace.show_trace:
-    print('Fire trace:\n{trace}'.format(trace=component_trace))
+    print('Fire trace:\n{trace}'.format(trace=component_trace),
+          file=sys.stderr)
     raise FireExit(0, component_trace)
   elif component_trace.show_help:
     result = component_trace.GetResult()
     print(
-        helputils.HelpString(result, component_trace, component_trace.verbose))
+        helputils.HelpString(result, component_trace, component_trace.verbose),
+        file=sys.stderr)
     raise FireExit(0, component_trace)
   else:
     _PrintResult(component_trace, verbose=component_trace.verbose)

fire/core_test.py

@@ -99,9 +99,9 @@ def testFireErrorMultipleValues(self):
     self.assertIsNotNone(error)
 
   def testPrintEmptyDict(self):
-    with self.assertStdoutMatches('{}'):
+    with self.assertOutputMatches(stdout='{}', stderr=None):
       core.Fire(tc.EmptyDictOutput, 'totally_empty')
-    with self.assertStdoutMatches('{}'):
+    with self.assertOutputMatches(stdout='{}', stderr=None):
       core.Fire(tc.EmptyDictOutput, 'nothing_printable')
 
 

fire/testutils.py

@@ -34,17 +34,44 @@ class BaseTestCase(unittest.TestCase):
   """Shared test case for Python Fire tests."""
 
   @contextlib.contextmanager
-  def assertStdoutMatches(self, regexp):
-    """Asserts that the context generates stdout matching regexp."""
-    stdout = six.StringIO()
-    with mock.patch.object(sys, 'stdout', stdout):
-      yield
-    value = stdout.getvalue()
-    if not re.search(regexp, value, re.DOTALL | re.MULTILINE):
-      raise AssertionError('Expected %r to match %r' % (value, regexp))
+  def assertOutputMatches(self, stdout='.*', stderr='.*', capture=True):
+    """Asserts that the context generates stdout and stderr matching regexps.
+
+    Note: If wrapped code raises an exception, stdout and stderr will not be
+      checked.
+
+    Args:
+      stdout: (str) regexp to match against stdout (None will check no stdout)
+      stderr: (str) regexp to match against stderr (None will check no stderr)
+      capture: (bool, default True) do not bubble up stdout or stderr
+    Yields:
+      Yields to the wrapped context.
+    """
+    stdout_fp = six.StringIO()
+    stderr_fp = six.StringIO()
+    try:
+      with mock.patch.object(sys, 'stdout', stdout_fp):
+        with mock.patch.object(sys, 'stderr', stderr_fp):
+          yield
+    finally:
+      if not capture:
+        sys.stdout.write(stdout_fp.getvalue())
+        sys.stderr.write(stderr_fp.getvalue())
+
+    for name, regexp, fp in [('stdout', stdout, stdout_fp),
+                             ('stderr', stderr, stderr_fp)]:
+      value = fp.getvalue()
+      if regexp is None:
+        if value:
+          raise AssertionError('%s: Expected no output. Got: %r' %
+                               (name, value))
+      else:
+        if not re.search(regexp, value, re.DOTALL | re.MULTILINE):
+          raise AssertionError('%s: Expected %r to match %r' %
+                               (name, value, regexp))
 
   @contextlib.contextmanager
-  def assertRaisesFireExit(self, code, regexp=None):
+  def assertRaisesFireExit(self, code, regexp='.*'):
     """Asserts that a FireExit error is raised in the context.
 
     Allows tests to check that Fire's wrapper around SystemExit is raised
@@ -56,23 +83,15 @@ def assertRaisesFireExit(self, code, regexp=None):
     Yields:
       Yields to the wrapped context.
     """
-    if regexp is None:
-      regexp = '.*'
-    with self.assertRaises(core.FireExit):
-      stdout = six.StringIO()
-      with mock.patch.object(sys, 'stdout', stdout):
+    with self.assertOutputMatches(stderr=regexp):
+      with self.assertRaises(core.FireExit):
         try:
           yield
         except core.FireExit as exc:
           if exc.code != code:
             raise AssertionError('Incorrect exit code: %r != %r' % (exc.code,
                                                                     code))
           self.assertIsInstance(exc.trace, trace.FireTrace)
-          stdout.flush()
-          stdout.seek(0)
-          value = stdout.getvalue()
-          if not re.search(regexp, value, re.DOTALL | re.MULTILINE):
-            raise AssertionError('Expected %r to match %r' % (value, regexp))
           raise
 
 

fire/testutils_test.py

@@ -0,0 +1,55 @@
+# Copyright (C) 2017 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Test the test utilities for Fire's tests."""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import sys
+
+import six
+
+from fire import testutils
+
+
+class TestTestUtils(testutils.BaseTestCase):
+  """Let's get meta."""
+
+  def testNoCheckOnException(self):
+    with self.assertRaises(ValueError):
+      with self.assertOutputMatches(stdout='blah'):
+        raise ValueError()
+
+  def testCheckStdoutOrStderrNone(self):
+    with six.assertRaisesRegex(self, AssertionError, 'stdout:'):
+      with self.assertOutputMatches(stdout=None):
+        print('blah')
+
+    with six.assertRaisesRegex(self, AssertionError, 'stderr:'):
+      with self.assertOutputMatches(stderr=None):
+        print('blah', file=sys.stderr)
+
+    with six.assertRaisesRegex(self, AssertionError, 'stderr:'):
+      with self.assertOutputMatches(stdout='apple', stderr=None):
+        print('apple')
+        print('blah', file=sys.stderr)
+
+  def testCorrectOrderingOfAssertRaises(self):
+    # Check to make sure FireExit tests are correct
+    with self.assertOutputMatches(stdout='Yep.*first.*second'):
+      with self.assertRaises(ValueError):
+        print('Yep, this is the first line.\nIt should match to the second')
+        raise ValueError()