How do you usually test rule-heavy logic with lots of edge cases?

[spellbeegamecom]

Hi everyone,

I’m working on some rule-heavy logic where behavior changes based on a growing set of conditions, and I’m finding it tricky to keep my JUnit tests both readable and complete. As more rules are added, the number of edge cases explodes, and tests start to feel repetitive.

This reminded me of something unrelated I was doing for unlimited spelling practice, where the real challenge isn’t a single case but validating that all rules are enforced correctly over many iterations. It made me think about testing strategy more generally.

When you’re dealing with logic like this, do you prefer parameterized tests, custom test data builders, or some other approach to avoid brittle or overly verbose test suites? Any patterns you’ve found especially effective?

[nchaugen]

do you prefer parameterized tests, custom test data builders

Yes, both of those.

@ParameterizedTest supports multiple value providers. I find tables are a nice way to make the variations of input and expected output readable. You can use @CsvSource and @CsvFileSource annotations for this.

Built-in support for argument conversion both implicit and explicit with @ConvertWith annotation will help turn the string values in the csv tables into more convenient test parameter types. Offloading this responsibility from the test methods make them easier to read and understand.

I also need to plug TableTest, a JUnit extension I have built to support readable tables and custom test data builders. It also supports collapsing multiple variations of input values with the same outcome into one row, something that might be helpful in your situation. ☺️