Finish Coverage (#30)

* Update test_basic.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

tests/test_basic.py

@@ -56,3 +56,6 @@ def dummy_callback(data):
     result = publisher.unsubscribe(callback_id)
     assert result == True
     assert callback_id not in publisher.callbacks
+
+    result = publisher.unsubscribe(callback_id)
+    assert result == False