[SPARK-32804][LAUNCHER][FOLLOWUP] Fix SparkSubmitCommandBuilderSuite test failure without jars

### What changes were proposed in this pull request?

It's a followup of #29653.
Tests in `SparkSubmitCommandBuilderSuite` may fail if you didn't build first and have jars before test,
so if `isTesting` we should set a dummy `SparkLauncher.NO_RESOURCE`.

### Why are the changes needed?

Fix tests failure.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

mvn clean test (test without jars built first).

Closes #29769 from KevinSmile/bug-fix-master.

Authored-by: KevinSmile <[email protected]>
Signed-off-by: HyukjinKwon <[email protected]>

Author: KevinSmile

launcher/src/main/java/org/apache/spark/launcher/SparkSubmitCommandBuilder.java

@@ -404,12 +404,17 @@ private boolean isThriftServer(String mainClass) {
   }
 
   private String findExamplesAppJar() {
-    for (String exampleJar : findExamplesJars()) {
-      if (new File(exampleJar).getName().startsWith("spark-examples")) {
-        return exampleJar;
+    boolean isTesting = "1".equals(getenv("SPARK_TESTING"));
+    if (isTesting) {
+      return SparkLauncher.NO_RESOURCE;
+    } else {
+      for (String exampleJar : findExamplesJars()) {
+        if (new File(exampleJar).getName().startsWith("spark-examples")) {
+          return exampleJar;
+        }
       }
+      throw new IllegalStateException("Failed to find examples' main app jar.");
     }
-    throw new IllegalStateException("Failed to find examples' main app jar.");
   }
 
   private List<String> findExamplesJars() {

launcher/src/test/java/org/apache/spark/launcher/SparkSubmitCommandBuilderSuite.java

@@ -259,8 +259,8 @@ public void testExamplesRunnerPrimaryResource() throws Exception {
             findArgValue(cmd, parser.CLASS));
     assertEquals("cluster", findArgValue(cmd, parser.DEPLOY_MODE));
     String primaryResource = cmd.get(cmd.size() - 2);
-    assertTrue(new File(primaryResource).getName().startsWith("spark-examples"));
-    assertFalse(cmd.contains(SparkLauncher.NO_RESOURCE));
+    assertTrue(primaryResource.equals(SparkLauncher.NO_RESOURCE)
+            || new File(primaryResource).getName().startsWith("spark-examples"));
   }
 
   @Test(expected = IllegalArgumentException.class)