Consolidate test validation

[stuebingerb]

Currently, validations in test functions are implemented in different ways:

• Using kluent, e.g.

  invoking {
      deserialize(schema.executeBlocking("{b{id, name, age}}"))
  } shouldThrow GraphQLError::class withMessage "Property id on B does not exist"
  

• Using custom implementations, e.g.

  expect<IllegalAccessException>("ILLEGAL ACCESS") {
      schema.executeBlocking("{black_mamba {item}}", context = context { +"LAKERS" }).also(::println)
  }
  

• Using hamcrest, e.g.

  assertThat(scenarioType["author"], nullValue())
  

This makes it unnecessarily complex and hard to maintain and should be consolidated, ideally towards a single, kotlin-native test library.

Ideas for alternatives:

• https://kotlinlang.org/docs/power-assert.html
• https://kotest.io/docs/assertions/assertions.html
• https://github.com/robstoll/atrium
• https://github.com/willowtreeapps/assertk
• https://github.com/assertj/assertj (since assertk is not that active and assertj works pretty well already)
• https://github.com/robfletcher/strikt (albeit not very active recently)

[stuebingerb]

Kluent is archived since January 2025 and should not be part of the target picture:
https://github.com/MarkusAmshove/Kluent

[stuebingerb]

Kotest it is, mainly out of gut feeling and lack of motivation to do a full-blown research.

Still, some reasoning for reference:

• Kotest is a well-known name in the Kotlin community
• Kotest has an active Github repository and has been around for a while
• Kotest has pretty readable assertions
• Kotest has built-in support for Json assertions
• Kotest is Kotlin native and supports Kotlin multiplatform, which might be interesting in the future
• Kotest has its own test runner, and could also be used as a replacement for JUnit in the future

For now I'd stick with JUnit, though, and only use the assertions part of Kotest.