haveElementAt-more-detail (#49)

kotest-assertions/kotest-assertions-core/src/commonMain/kotlin/io/kotest/matchers/collections/matchers.kt

@@ -15,12 +15,31 @@ fun <T> Array<T>.shouldNotHaveElementAt(index: Int, element: T) = asList().shoul
 fun <T> List<T>.shouldNotHaveElementAt(index: Int, element: T) = this shouldNot haveElementAt(index, element)
 
 fun <T, L : List<T>> haveElementAt(index: Int, element: T) = object : Matcher<L> {
-   override fun test(value: L) =
-      MatcherResult(
-         index < value.size && value[index] == element,
-         { "Collection ${value.print().value} should contain ${element.print().value} at index $index" },
+   override fun test(value: L): MatcherResult {
+      val passed = index < value.size && value[index] == element
+      val listTooShortMsg = if(index < value.size) "" else "But it is too short: only ${value.size} elements"
+      val unexpectedElementMsg = when {
+         passed -> ""
+         index < value.size -> "Expected: <${value[index].print().value}>, but was <${element.print().value}>"
+         else -> ""
+      }
+      val indexesForElement = value.mapIndexedNotNull { index, current ->
+         if(current == element) index else null
+      }
+      val indexesForElementMsg = if(passed || indexesForElement.isEmpty())
+         ""
+      else "Element was found at index(es): ${indexesForElement.print().value}"
+      val additionalDescriptions = listOf(listTooShortMsg, unexpectedElementMsg, indexesForElementMsg).filter {
+         it.isNotEmpty()
+      }
+      val additionalDescriptionsMsg = if(additionalDescriptions.isEmpty()) ""
+      else "\n${additionalDescriptions.joinToString("\n")}"
+      return MatcherResult(
+         passed,
+         { "Collection ${value.print().value} should contain ${element.print().value} at index $index$additionalDescriptionsMsg" },
          { "Collection ${value.print().value} should not contain ${element.print().value} at index $index" }
       )
+   }
 }
 
 infix fun <T> Iterable<T>.shouldExist(p: (T) -> Boolean) = toList().shouldExist(p)

kotest-assertions/kotest-assertions-core/src/jvmTest/kotlin/com/sksamuel/kotest/matchers/collections/CollectionMatchersTest.kt

@@ -72,6 +72,7 @@ import io.kotest.matchers.shouldBe
 import io.kotest.matchers.shouldHave
 import io.kotest.matchers.shouldNot
 import io.kotest.matchers.shouldNotHave
+import io.kotest.matchers.string.shouldContain
 import io.kotest.matchers.throwable.shouldHaveMessage
 
 class CollectionMatchersTest : WordSpec() {
@@ -143,6 +144,40 @@ class CollectionMatchersTest : WordSpec() {
             tests should haveElementAt(0, TestSealed.Test1("test1"))
             tests.shouldHaveElementAt(1, TestSealed.Test2(2))
          }
+         "print if list is too short" {
+            shouldThrowAny {
+               listOf("a", "b", "c").shouldHaveElementAt(3, "d")
+            }.message shouldBe """
+            |Collection ["a", "b", "c"] should contain "d" at index 3
+            |But it is too short: only 3 elements
+            """.trimMargin()
+         }
+         "print if element does not match" {
+            shouldThrowAny {
+               listOf("a", "b", "c").shouldHaveElementAt(2, "d")
+            }.message shouldBe """
+            |Collection ["a", "b", "c"] should contain "d" at index 2
+            |Expected: <"c">, but was <"d">
+            """.trimMargin()
+         }
+         "print if element found at another index" {
+            shouldThrowAny {
+               listOf("a", "b", "c").shouldHaveElementAt(2, "b")
+            }.message shouldBe """
+            |Collection ["a", "b", "c"] should contain "b" at index 2
+            |Expected: <"c">, but was <"b">
+            |Element was found at index(es): [1]
+            """.trimMargin()
+         }
+         "print if element found at multiple other indexes" {
+            shouldThrowAny {
+               listOf("a", "b", "c", "b").shouldHaveElementAt(2, "b")
+            }.message shouldBe """
+            |Collection ["a", "b", "c", "b"] should contain "b" at index 2
+            |Expected: <"c">, but was <"b">
+            |Element was found at index(es): [1, 3]
+            """.trimMargin()
+         }
       }
 
       "containNull()" should {