No easy way to change number of tests

Currently, there's not an easy way to change the number of tests run from the default (100). Even if you do reach in and change it manually, it doesn't change the successful test output, which as far as I know is hardcoded to "✓ passed 100 tests."

It would be nice to change the number of tests for tests where a potential failure case might be particularly rare.

Start by locating where the default of 100 tests and the successful output string are defined. Trace how test counts are configured and reported, then make the count adjustable and ensure the success message reflects the selected number; verify the existing test behavior afterward.

Written by the indexing model from the issue text.