force that one has to write notToEqualNull instead of assertionCreatorOrNull?

[robstoll]

some context:
In the very beginning of Atrium we were more strict regarding nullability and one was not able to write: expect(nullableInt).toEqual(1) one could only use notToEqualNull and toEqual(null) for nullable subjects. Those two methods were defined on a NullableExpect. i.e. one had to writeexpect(nullableInt).notToBeNull().toEqual(1) instead.

Because we ran into ambiguity issues with expect(listWithNullableElements).inOrder...entries(null, { ... }) we resorted to have only one overload with an nullable assertionCreatorLambda.

By now, we no longer have a NullableExpect and thus we could think about making assertionCreatorOrNull non-nullable and instead force the user to write notToEqualNull in case of a nullable-element inside the assertionCreator.

This would have the advantage, that the null-case does no longer feel alien to the rest.

This has one drawback though. Where one was able to write

expect(1,2,3,3, null).toContain({ toBeGreaterThan(3) }, { toBeGreaterThan(2) })

now has to write

expect(1,2,3,3, null).toContain(
  { notToEqual(null) { toBeGreaterThan(3) } },
  { notToEqual(null) { toBeGreaterThan(2) } }
)

We could help out by providing extra overloads for nullable elements something like:

expect(1,2,3,3, null).toContainNonNullable({ toBeGreaterThan(3) }, { toBeGreaterThan(2) })

But as long as Kotlin doesn't have lower bounds they would also show up for non-nullable subjects and that would be ugly IMO.

Since this would be a breaking change, we should carefully consider to actually change this.