From 5a79a8817d5ac303d010468c2a99781502a57f6b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ionel=20Cristian=20M=C4=83rie=C8=99?= <contact@ionelmc.ro>
Date: Sun, 30 Jul 2017 18:48:35 +0300
Subject: [PATCH] Change of behavior: when report generation fails log a
 warning instead. This is consistent with other kinds of failures (like
 misconfigration) that result in no coverage data/results. Closes #161.

---
 src/pytest_cov/plugin.py | 20 +++++++++++---------
 tests/test_pytest_cov.py |  4 ++--
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/src/pytest_cov/plugin.py b/src/pytest_cov/plugin.py
index 05ac0393..2ddf61ea 100644
--- a/src/pytest_cov/plugin.py
+++ b/src/pytest_cov/plugin.py
@@ -238,9 +238,11 @@ def pytest_runtestloop(self, session):
             try:
                 self.cov_total = self.cov_controller.summary(self.cov_report)
             except CoverageException as exc:
-                raise pytest.UsageError(
-                    'Failed to generate report: %s\n' % exc
-                )
+                message = 'Failed to generate report: %s\n' % exc
+                session.config.pluginmanager.getplugin("terminalreporter").write(
+                    'WARNING: %s\n' % message, red=True, bold=True)
+                session.config.warn(code='COV-2', message=message)
+                self.cov_total = 0
             assert self.cov_total is not None, 'Test coverage should never be `None`'
             if self._failed_cov_total():
                 # make sure we get the EXIT_TESTSFAILED exit code
@@ -248,9 +250,9 @@ def pytest_runtestloop(self, session):
 
     def pytest_terminal_summary(self, terminalreporter):
         if self._disabled:
-            msg = 'Coverage disabled via --no-cov switch!'
-            terminalreporter.write('WARNING: %s\n' % msg, red=True, bold=True)
-            terminalreporter.config.warn(code='COV-U1', message=msg)
+            message = 'Coverage disabled via --no-cov switch!'
+            terminalreporter.write('WARNING: %s\n' % message, red=True, bold=True)
+            terminalreporter.config.warn(code='COV-1', message=message)
             return
         if self.cov_controller is None:
             return
@@ -264,19 +266,19 @@ def pytest_terminal_summary(self, terminalreporter):
         if self.options.cov_fail_under is not None and self.options.cov_fail_under > 0:
             if self.cov_total < self.options.cov_fail_under:
                 markup = {'red': True, 'bold': True}
-                msg = (
+                message = (
                     'FAIL Required test coverage of %d%% not '
                     'reached. Total coverage: %.2f%%\n'
                     % (self.options.cov_fail_under, self.cov_total)
                 )
             else:
                 markup = {'green': True}
-                msg = (
+                message = (
                     'Required test coverage of %d%% '
                     'reached. Total coverage: %.2f%%\n'
                     % (self.options.cov_fail_under, self.cov_total)
                 )
-            terminalreporter.write(msg, **markup)
+            terminalreporter.write(message, **markup)
 
     def pytest_runtest_setup(self, item):
         if os.getpid() != self.pid:
diff --git a/tests/test_pytest_cov.py b/tests/test_pytest_cov.py
index 9a39289b..39916532 100644
--- a/tests/test_pytest_cov.py
+++ b/tests/test_pytest_cov.py
@@ -706,8 +706,8 @@ def test_invalid_coverage_source(testdir):
         assert result.ret == 0
     else:
         # newer `coverage report` errors on missing imports
-        result.stderr.fnmatch_lines([
-            'ERROR: Failed to generate report: No data to report.',
+        result.stdout.fnmatch_lines([
+            '*Failed to generate report: No data to report.',
         ])
         assert result.ret != 0