Allow @Ignore on junit test classes

Currently a test class annotated with `@Ignore` will cause the test
runner to fail with

```
Exception in thread "main" java.lang.IllegalArgumentException: Top test must be a suite
	at com.google.testing.junit.runner.junit4.JUnit4TestModelBuilder.get(JUnit4TestModelBuilder.java:53)
```

This change treats classes with no tests (either no @Test annotations or
@Ignore at class level) as an empty test suite. The main motivation
behind this is allowing an entire test class to be ignored (e.g. to
quickly deal with a flaky test) without having to modify the BUILD file.
This is desirable in order to reduce the likelihood that a developer
forgets to update the BUILD file when removing the `@Ignore` annotation.

This pull request overrides the previous pull request
https://github.com/bazelbuild/bazel/pull/4073

Closes #4293.

PiperOrigin-RevId: 188850828

2 files changed, 30 insertions, 8 deletions

diff --git a/src/java_tools/junitrunner/java/com/google/testing/junit/runner/junit4/JUnit4TestModelBuilder.java b/src/java_tools/junitrunner/java/com/google/testing/junit/runner/junit4/JUnit4TestModelBuilder.java
index 56d57c1d86..75199cf144 100644
--- a/src/java_tools/junitrunner/java/com/google/testing/junit/runner/junit4/JUnit4TestModelBuilder.java
+++ b/src/java_tools/junitrunner/java/com/google/testing/junit/runner/junit4/JUnit4TestModelBuilder.java
@@ -17,12 +17,10 @@ package com.google.testing.junit.runner.junit4;
 import com.google.testing.junit.runner.model.TestSuiteModel;
 import com.google.testing.junit.runner.model.TestSuiteModel.Builder;
 import com.google.testing.junit.runner.util.Supplier;
-
-import org.junit.runner.Description;
-import org.junit.runner.Request;
-
 import javax.inject.Inject;
 import javax.inject.Singleton;
+import org.junit.runner.Description;
+import org.junit.runner.Request;
 
 /**
  * Builds a {@link TestSuiteModel} for JUnit4 tests.
@@ -49,9 +47,12 @@ class JUnit4TestModelBuilder implements Supplier<TestSuiteModel> {
   @Override
   public TestSuiteModel get() {
     Description root = request.getRunner().getDescription();
+    // A test class annotated with @Ignore effectively has no test methods,
+    // which is what isSuite() tests for.
     if (!root.isSuite()) {
-      throw new IllegalArgumentException("Top test must be a suite");
+      return builder.build(suiteName);
+    } else {
+      return builder.build(suiteName, root);
     }
-    return builder.build(suiteName, root);
   }
 }
diff --git a/src/java_tools/junitrunner/javatests/com/google/testing/junit/runner/junit4/JUnit4TestModelBuilderTest.java b/src/java_tools/junitrunner/javatests/com/google/testing/junit/runner/junit4/JUnit4TestModelBuilderTest.java
index b409163617..c1a4efbd00 100644
--- a/src/java_tools/junitrunner/javatests/com/google/testing/junit/runner/junit4/JUnit4TestModelBuilderTest.java
+++ b/src/java_tools/junitrunner/javatests/com/google/testing/junit/runner/junit4/JUnit4TestModelBuilderTest.java
@@ -32,6 +32,7 @@ import com.google.testing.junit.runner.sharding.testing.StubShardingEnvironment;
 import com.google.testing.junit.runner.util.FakeTicker;
 import com.google.testing.junit.runner.util.Ticker;
 import java.util.List;
+import org.junit.Ignore;
 import org.junit.Test;
 import org.junit.runner.Description;
 import org.junit.runner.Request;
@@ -92,6 +93,18 @@ public class JUnit4TestModelBuilderTest {
   }
 
   @Test
+  public void testCreateModel_topLevelIgnore() throws Exception {
+    Class<?> testClass = SampleTestCaseWithTopLevelIgnore.class;
+    Request request = Request.classWithoutSuiteMethod(testClass);
+    String testClassName = testClass.getCanonicalName();
+    JUnit4TestModelBuilder modelBuilder =
+        builder(request, testClassName, stubShardingEnvironment, null, xmlResultWriter);
+
+    TestSuiteModel testSuiteModel = modelBuilder.get();
+    assertThat(testSuiteModel.getNumTestCases()).isEqualTo(0);
+  }
+
+  @Test
   public void testCreateModel_singleTestClass() throws Exception {
     Class<?> testClass = SampleTestCaseWithTwoTests.class;
     Request request = Request.classWithoutSuiteMethod(testClass);
@@ -140,7 +153,6 @@ public class JUnit4TestModelBuilderTest {
     assertThat(model.getNumTestCases()).isEqualTo(1);
   }
 
-
   /** Sample test case with two tests. */
   @RunWith(JUnit4.class)
   public static class SampleTestCaseWithTwoTests {
@@ -153,6 +165,16 @@ public class JUnit4TestModelBuilderTest {
     }
   }
 
+  /** Sample test case with top level @Ignore */
+  @Ignore
+  @RunWith(JUnit4.class)
+  public static class SampleTestCaseWithTopLevelIgnore {
+    @Test
+    public void testOne() {}
+
+    @Test
+    public void testTwo() {}
+  }
 
   /** Sample test case with one test. */
   @RunWith(JUnit4.class)
@@ -162,7 +184,6 @@ public class JUnit4TestModelBuilderTest {
     }
   }
 
-
   /** Sample suite with one test. */
   @RunWith(Suite.class)
   @SuiteClasses(SampleTestCaseWithOneTest.class)