add a coveragerc

.coveragerc

@@ -0,0 +1,21 @@
+[run]
+branch = True
+source = traitsui
+omit = */tests/*
+
+[report]
+# Regexes for lines to exclude from consideration
+exclude_lines =
+    # Have to re-enable the standard pragma
+    pragma: no cover
+
+    # Don't complain about missing debug-only code:
+    def __repr__
+
+    # Don't complain if tests don't hit defensive assertion code:
+    raise AssertionError
+    raise NotImplementedError
+
+    if __name__ == .__main__.:
+
+ignore_errors = True