Uniformize message for failing legacy functional tests

Author: Pierre-Sassoulas

doc/development_guide/contribute.rst

@@ -162,12 +162,14 @@ During development, it's sometimes helpful to run all functional tests in your
 current environment in order to have faster feedback. Run from Pylint root directory with::
 
     python tests/test_functional.py
+    python tests/test_func.py # For legacy functional tests
 
 You can use all the options you would use for pytest, for example `-k "test_functional[len_checks]"`.
 It is also possible to update the expected output instead of using it for comparison, by appending
 `--update-functional-output` to the command line::
 
     python tests/test_functional.py --update-functional-output -k "test_functional[len_checks]"
+    python tests/test_func.py --update-functional-output # For legacy functional tests
 
 .. _`Closing issues via commit messages`: https://help.github.com/articles/closing-issues-via-commit-messages/
 .. _`About pull requests`: https://help.github.com/articles/using-pull-requests/

tests/test_func.py

@@ -61,7 +61,15 @@ def _test_functionality(self):
         self._test(tocheck)
 
     def _check_result(self, got):
-        assert self._get_expected().strip() + "\n" == got.strip() + "\n"
+        error_msg = (
+            "Wrong output for '{_file}':\n"
+            "You can update the expected output automatically with: '"
+            "python tests/test_func.py {update_option}'\n\n".format(
+                update_option=UPDATE_OPTION,
+                _file=self.output,
+            )
+        )
+        assert self._get_expected() == got, error_msg
 
     def _test(self, tocheck):
         if INFO_TEST_RGX.match(self.module):
@@ -92,14 +100,15 @@ def _get_expected(self):
 
 class LintTestUpdate(LintTestUsingModule):
     def _check_result(self, got):
-        if self._has_output():
-            try:
-                expected = self._get_expected()
-            except OSError:
-                expected = ""
-            if got != expected:
-                with open(self.output, "w") as fobj:
-                    fobj.write(got)
+        if not self._has_output():
+            return
+        try:
+            expected = self._get_expected()
+        except OSError:
+            expected = ""
+        if got != expected:
+            with open(self.output, "w") as f:
+                f.write(got)
 
 
 def gen_tests(filter_rgx):