testutils: Add a context manager to capture stderr

and use it to test the help output

1 files changed, 29 insertions, 0 deletions

diff --git a/tests/testutils/capture.py b/tests/testutils/capture.py
new file mode 100644
index 0000000..60d5a12
--- /dev/null
+++ b/tests/testutils/capture.py
@@ -0,0 +1,29 @@
+# vim: set fileencoding=utf-8 :
+
+import sys
+from contextlib import contextmanager
+from StringIO import StringIO
+
+
+class StderrCapture(StringIO):
+    def save(self):
+        self.safed = sys.stderr
+        sys.stderr = self
+
+    def restore(self):
+        if self.safed is not None:
+            sys.stderr = self.safed
+            self.safed = None
+
+    def output(self):
+        self.seek(0)
+        return self.read()
+
+
+@contextmanager
+def capture_stderr():
+    """Capture an output and return it's content"""
+    c = StderrCapture()
+    c.save()
+    yield c
+    c.restore()