[BAEL-18364] move spring-rest-*** articles - 1

java-collections-maps/src/test/java/com/baeldung/map/KeyCheckUnitTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.map;
+
+import org.junit.Test;
+
+import java.util.Collections;
+import java.util.Map;
+
+import static org.junit.Assert.*;
+
+public class KeyCheckUnitTest {
+
+    @Test
+    public void whenKeyIsPresent_thenContainsKeyReturnsTrue() {
+        Map<String, String> map = Collections.singletonMap("key", "value");
+
+        assertTrue(map.containsKey("key"));
+        assertFalse(map.containsKey("missing"));
+    }
+
+    @Test
+    public void whenKeyHasNullValue_thenGetStillWorks() {
+        Map<String, String> map = Collections.singletonMap("nothing", null);
+
+        assertTrue(map.containsKey("nothing"));
+        assertNull(map.get("nothing"));
+    }
+}