Add unit tests

Author: aboitreaud

dd-java-agent/instrumentation/spark/spark-common/src/main/java/datadog/trace/instrumentation/spark/EmrUtils.java

@@ -8,7 +8,7 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-/** Extracts the AWS EMR Step ID from the working directory name (e.g. {@code s-0039...}). */
+/** Extracts the AWS EMR Step ID from the working directory name (e.g. s-07767992IY7VC5NVV854). */
 class EmrUtils {
 
   private static final Logger log = LoggerFactory.getLogger(EmrUtils.class);

dd-java-agent/instrumentation/spark/spark-common/src/test/java/datadog/trace/instrumentation/spark/EmrUtilsTest.java

@@ -0,0 +1,41 @@
+package datadog.trace.instrumentation.spark;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class EmrUtilsTest {
+
+  private String originalUserDir;
+
+  @BeforeEach
+  void saveUserDir() {
+    originalUserDir = System.getProperty("user.dir");
+  }
+
+  @AfterEach
+  void restoreUserDir() {
+    System.setProperty("user.dir", originalUserDir);
+  }
+
+  @Test
+  void returnsStepIdWhenWorkdirMatchesEmrPattern() {
+    System.setProperty("user.dir", "/mnt/var/lib/hadoop/steps/s-07767992IY7VC5NVV854");
+    assertEquals("s-07767992IY7VC5NVV854", EmrUtils.getEmrStepId());
+  }
+
+  @Test
+  void returnsNullWhenWorkdirDoesNotMatchEmrPattern() {
+    System.setProperty("user.dir", "/home/hadoop");
+    assertNull(EmrUtils.getEmrStepId());
+  }
+
+  @Test
+  void returnsNullForApplicationIdWorkdir() {
+    System.setProperty("user.dir", "/home/hadoop/application_1234567890_0001");
+    assertNull(EmrUtils.getEmrStepId());
+  }
+}