}
        def class2 = Stub(TestClassResult) {
            getClassName() >> 'class-2'
        }

        when:
        provider.visitClasses(action)

        then:
        1 * provider1.visitClasses(_) >> { Action a -> a.execute(class1) }
        1 * provider2.visitClasses(_) >> { Action a -> a.execute(class2) }
        // TODO(radimk): should not assume order
        1 * action.execute(_) >> { TestClassResult r ->

import java.io.Closeable;
import java.io.Writer;

public interface TestResultsProvider extends Closeable {
    /**
     * Writes the output of the given test to the given writer. This method must be called only after {@link #visitClasses(org.gradle.api.Action)}.
     *
     * Writes all output for the test class.
     */
    void writeAllOutput(long classId, TestOutputEvent.Destination destination, Writer writer);

    public AggregateTestResultsProvider(Iterable<TestResultsProvider> providers) {
        this.providers = providers;
    }

    @Override
    public void visitClasses(final Action<? super TestClassResult> visitor) {
        final Map<String, OverlaidIdProxyingTestClassResult> aggregatedTestResults = new LinkedHashMap<String, OverlaidIdProxyingTestClassResult>();

        def barTest = new TestClassResult(2, 'BarTest', 100)
            .add(new TestMethodResult(2, "bar"))
            .add(new TestMethodResult(3, "bar2"))

        resultsProvider.visitClasses(_) >> { Action action ->
            action.execute(fooTest)
            action.execute(barTest)
        }

        when:
        generator.generate()

        then:

            public void execute(TestOutputStore.Reader reader) {
                reader.writeTestOutput(classId, testId, destination, writer);
            }
        });
    }

    @Override
    public void visitClasses(final Action<? super TestClassResult> visitor) {
        resultSerializer.read(visitor);
    }

            public void execute(TestOutputStore.Reader reader) {
                reader.writeTestOutput(classId, testId, destination, writer);
            }
        });
    }

    @Override
    public void visitClasses(final Action<? super TestClassResult> visitor) {
        for (TestClassResult result : results) {
            visitor.execute(result);
        }
    }

    @Override
    public boolean isHasResults() {

            @Override
            public void execute(final BuildOperationQueue<JUnitXmlReportFileGenerator> queue) {
                testResultsProvider.visitClasses(new Action<TestClassResult>() {
                    @Override
                    public void execute(final TestClassResult result) {

            if (event.testOutputEvent.destination == destination && (allClassOutput || testId == event.testId)) {
                writer.append(event.testOutputEvent.message)
            }
        }
    }

    void visitClasses(Action<? super TestClassResult> visitor) {
        testClasses.values().each {
            visitor.execute(it)
        }
    }

    boolean isHasResults() {
        !testClasses.isEmpty()
    }

    }

    private AllTestResults loadModelFromProvider(TestResultsProvider resultsProvider) {
        final AllTestResults model = new AllTestResults();
        resultsProvider.visitClasses(new Action<TestClassResult>() {
            @Override
            public void execute(TestClassResult classResult) {

            }
        }
    }

    def results(TestFile file) {
        return new HtmlTestResultsFixture(file)
    }

    def emptyResultSet() {
        _ * testResultProvider.visitClasses(_)
    }