Write better tests

[langmore]

I (langmore) made some mistakes when writing initial test suites, and future tests could be improved.

Test behavior, not implementation.

• Test the public API in more depth.
• Test private functions/methods only when necessary. These tests are hard to maintain and have no reason to hold up under refactoring...the most important time for a test to hold up is when you refactor.

Use descriptive test names

• The test name should make it clear what use case the test is testing.