Capture output of CallbackRegistry exception test.

QuLogic · QuLogic · commit 993176eb0ea7 · 2020-08-21T21:04:58.000-04:00
If running `pytest -s`, the default exception handler will print out the
traceback, appearing as if there were an error. But this is exactly what
this test is checking, so capture output and check it.
diff --git a/lib/matplotlib/tests/test_cbook.py b/lib/matplotlib/tests/test_cbook.py
@@ -226,16 +226,23 @@ def test_pickling(self):
                        "callbacks")
 
 
-def test_callbackregistry_default_exception_handler(monkeypatch):
+def test_callbackregistry_default_exception_handler(capsys, monkeypatch):
     cb = cbook.CallbackRegistry()
     cb.connect("foo", lambda: None)
+
     monkeypatch.setattr(
         cbook, "_get_running_interactive_framework", lambda: None)
     with pytest.raises(TypeError):
         cb.process("foo", "argument mismatch")
+    outerr = capsys.readouterr()
+    assert outerr.out == outerr.err == ""
+
     monkeypatch.setattr(
         cbook, "_get_running_interactive_framework", lambda: "not-none")
     cb.process("foo", "argument mismatch")  # No error in that case.
+    outerr = capsys.readouterr()
+    assert outerr.out == ""
+    assert "takes 0 positional arguments but 1 was given" in outerr.err
 
 
 def raising_cb_reg(func):
