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 map = Collections.singletonMap("key", "value"); assertTrue(map.containsKey("key")); assertFalse(map.containsKey("missing")); } @Test public void whenKeyHasNullValue_thenGetStillWorks() { Map map = Collections.singletonMap("nothing", null); assertTrue(map.containsKey("nothing")); assertNull(map.get("nothing")); } }