Add basic test for har_extractor

test/mitmproxy/test_har_extractor.py

@@ -0,0 +1,10 @@
+from . import tutils
+
+from mitmproxy import script, flow
+from examples import har_extractor
+
+
+def test_start():
+    fm = flow.FlowMaster(None, flow.State())
+    ctx = script.ScriptContext(fm)
+    tutils.raises(ValueError, har_extractor.start, ctx, [])