Rename these tests so failures explain themselves

When a red CI run tells you `test_handler_2` failed and nothing more.

Rename the tests below so that the name alone explains a failure.

Rules:
1. Each name should state the condition and the expected behaviour: what is being tested, under what circumstance, and what should happen.
2. Remove "test", "works", "correctly", "should be fine" and the word "and" where it hides two assertions.
3. Match the naming convention already used in the file. Tell me what that convention appears to be.
4. Where a test name cannot be written clearly, the test is probably doing too much. Say which ones, and how to split them.

Output a table: current name, proposed name, and the failure message a developer would see at 2am.

Tests:

Reviewing existing tests. Judging naming, mocking, and whether a test asserts behaviour or just the implementation.