Fix some coding and style issues.
1. Treat "testcase" as one word. This is consistent with ClusterFuzz.
2. Treat "stacktrace" as one word. This is consistent with ClusterFuzz.
3. Fix spelling of comments and words in code.
4. Use descriptive style docstrings and remove unnecessary clutter
(e.g. "Test the functionality of foo_function function in bar module"
becomes "Tests foo_function."
5. Use JSON for a list needed in testing instead of pickle.
jonathanmetzman