add unit test for timestamp to auditstamp mapper test

Author: yoonhyejin

datahub-graphql-core/src/test/java/com/linkedin/datahub/graphql/types/common/mappers/TimeStampToAuditStampMapperTest.java

@@ -0,0 +1,46 @@
+package com.linkedin.datahub.graphql.types.common.mappers;
+
+import static org.testng.Assert.*;
+
+import com.linkedin.common.TimeStamp;
+import com.linkedin.common.urn.Urn;
+import com.linkedin.datahub.graphql.generated.AuditStamp;
+import org.testng.annotations.Test;
+
+public class TimeStampToAuditStampMapperTest {
+
+  private static final String TEST_ACTOR_URN = "urn:li:corpuser:testUser";
+  private static final long TEST_TIME = 1234567890L;
+
+  @Test
+  public void testMapWithActor() throws Exception {
+    TimeStamp input = new TimeStamp();
+    input.setTime(TEST_TIME);
+    input.setActor(Urn.createFromString(TEST_ACTOR_URN));
+
+    AuditStamp result = TimeStampToAuditStampMapper.map(null, input);
+
+    assertNotNull(result);
+    assertEquals(result.getTime().longValue(), TEST_TIME);
+    assertEquals(result.getActor(), TEST_ACTOR_URN);
+  }
+
+  @Test
+  public void testMapWithoutActor() {
+    TimeStamp input = new TimeStamp();
+    input.setTime(TEST_TIME);
+
+    AuditStamp result = TimeStampToAuditStampMapper.map(null, input);
+
+    assertNotNull(result);
+    assertEquals(result.getTime().longValue(), TEST_TIME);
+    assertNull(result.getActor());
+  }
+
+  @Test
+  public void testMapNull() {
+    AuditStamp result = TimeStampToAuditStampMapper.map(null, null);
+    
+    assertNull(result);
+  }
+}