singleElement-more-info (#61)

kotest · Apr 26, 2024 · e5ce1cf · e5ce1cf
1 parent b612160
commit e5ce1cf
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Showing 2 changed files with 12 additions and 2 deletions.
diff --git a/...est-assertions-core/src/commonMain/kotlin/io/kotest/matchers/collections/singleElement.kt b/...est-assertions-core/src/commonMain/kotlin/io/kotest/matchers/collections/singleElement.kt
@@ -40,9 +40,15 @@ fun <T> singleElement(t: T): Matcher<Collection<T>> = object : Matcher<Collectio
             expected = t.print().value,
          )
       } else {
+         val elementFoundAtIndexes = value.mapIndexedNotNull {
+            index, element ->
+            if(element == t) index else null
+         }
+         val foundAtMessage = if(elementFoundAtIndexes.isEmpty()) "Element not found in collection"
+            else "Element found at index(es): ${elementFoundAtIndexes.print().value}"
          MatcherResult(
             passed = false,
-            failureMessageFn = { "Collection should be a single element of $t but has ${value.size} elements: ${value.print().value}" },
+            failureMessageFn = { "Collection should be a single element of $t but has ${value.size} elements: ${value.print().value}. $foundAtMessage." },
             negatedFailureMessageFn = { "Collection should not be a single element of $t" },
          )
       }

diff --git a/...ore/src/jvmTest/kotlin/com/sksamuel/kotest/matchers/collections/CollectionMatchersTest.kt b/...ore/src/jvmTest/kotlin/com/sksamuel/kotest/matchers/collections/CollectionMatchersTest.kt
@@ -250,7 +250,11 @@ class CollectionMatchersTest : WordSpec() {
 
             shouldThrow<AssertionError> {
                listOf(1, 2) shouldBe singleElement(2)
-            }.shouldHaveMessage("Collection should be a single element of 2 but has 2 elements: [1, 2]")
+            }.shouldHaveMessage("Collection should be a single element of 2 but has 2 elements: [1, 2]. Element found at index(es): [1].")
+
+            shouldThrow<AssertionError> {
+               listOf(1, 2) shouldBe singleElement(3)
+            }.shouldHaveMessage("Collection should be a single element of 3 but has 2 elements: [1, 2]. Element not found in collection.")
          }
       }