What's the best way to write a custom matcher for ...

# kotest

[kierans777]

What's the best way to write a custom matcher for a composite type? I think this should be added to the docs. For example

data class Person(name: String, address: String)

fun aPerson(name: String, address: String): Matcher<Person> =
  object: Matcher<Person> {
    override fun test(value: Person): MatcherResult {
      if (value.name != name) {
        return MatcherResult(false, { "${value.name} should be $name" }, { "${value.name} should not be $name" })
      }

      if (value.address != address) {
        return MatcherResult(false, { "${value.address} should be $address" }, { "${value.address} should not be $address" })
      }

      return MatcherResult(true, { "person is correct" }, { "person is not correct" })
    }
  }

Is there a better way that I'm missing?

[sam]

You could tidy it up by using a when rather than if's, but that looks ok to me

[kierans777]

Thanks @sam

[Pavel Meledin]

@kierans777 as a possible improvement: you could accept from outside not only exact strings but matches. This way you’ll:
1. reuse existing matchers
2. make more flexible aPerson matcher that for instance could accept a matcher that would compare not only for exact equality but that either of fields might contain some sub string or check length of the field, etc.

[sam]

It should be possible to add some matcher combinators to Kotest too. So you can do Matcher.compose(nameMatcher, addressMatcher) kinda thing.

[sam]

https://github.com/kotest/kotest/issues/2845

[kierans777]

As I do a lot more FP with Arrow I'd love to compose matchers together. I wrote my own little setup that takes a list of functions, and returns the first failed MatcherResult or a success.

[sam]

I would welcome a pr :)