Ok, here's an example 🙂

shouldThrow<AssertionError> {
               assertSoftly {
                  mapOf("key" to "hi") should matchAll("key" to { it shouldHaveLength 4 })
               }
            }.message shouldBe """
               Expected map to match all assertions. Missing keys were=[key], Mismatched values were=[(key, "hi" should have length 4, but instead was 2)].
            """.trimIndent()

This test fails with :

Expected :"Expected map to match all assertions. Missing keys were=[key], Mismatched values were=[(key, "hi" should have length 4, but instead was 2)]."
Actual   :""hi" should have length 4, but instead was 2"

Due to the message being wrong. The reason the message is wrong is because the inner

shouldHaveLength

matcher is not throwing (since we're inside

assertSoftly

) and then when the assertSoftly block terminates it throws all captured assertion errors, just giving us the underlying error.

I pushed a commit with the example on your branch. Feel free to revert/change it if you want.