Add containsKey assertion for Map

Author: Goooler

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+- Add `containsKey` for `Map`.
+
 ### Changed
 - renamed `prop` to `having` as part of effort to unify API naming, old name is deprecated.
 - renamed `suspendCall` to `having` as part of effort to unify API naming, old name is deprecated.

assertk/src/commonMain/kotlin/assertk/assertions/map.kt

@@ -74,6 +74,14 @@ fun <K, V> Assert<Map<K, V>>.contains(element: Pair<K, V>) {
     contains(element.first, element.second)
 }
 
+/**
+ * Asserts the map contains the expected key.
+ */
+fun <K, V> Assert<Map<K, V>>.containsKey(key: K) = given {
+    if (it.containsKey(key)) return
+    expected("to contain key:${show(key)} but was:${show(it.keys)}")
+}
+
 /**
  * Asserts the map contains at least the expected elements. The map may also contain additional elements.
  * @see [containsNone]

assertk/src/commonTest/kotlin/test/assertk/assertions/MapTest.kt

@@ -28,6 +28,19 @@ class MapTest {
         }
         assertEquals("expected to contain:<{\"one\"=null}> but was:<{}>", error.message)
     }
+
+    @Test
+    fun containsKey_key_present_passes() {
+        assertThat(mapOf("one" to 1)).containsKey("one")
+    }
+
+    @Test
+    fun containsKey_key_missing_fails() {
+        val error = assertFailsWith<AssertionError> {
+            assertThat(mapOf("one" to 1)).containsKey("two")
+        }
+        assertEquals("expected to contain key:<\"two\"> but was:<[\"one\"]>", error.message)
+    }
     //endregion
 
     //region doesNotContain