Aggregate junit report into one file (#1056)

Some systems require junit report to be in a single file. For example `bazel` https://bazel.build/reference/test-encyclopedia needs single file to be available in `XML_OUTPUT_FILE` path.

To avoid implementing junit aggregation in pkl wrappers in different places this PR instead adds a `--junit-aggregate-reports` flag to return all junit reports as a single file.

Additional flag `--junit-aggregate-suite-name` is added to allow overriding global test suite name from default `pkl-tests`

pkl-core/src/main/java/org/pkl/core/stdlib/test/report/JUnitReport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,7 +18,9 @@ package org.pkl.core.stdlib.test.report;
 import java.io.IOException;
 import java.io.Writer;
 import java.util.ArrayList;
+import java.util.List;
 import java.util.function.Consumer;
+import java.util.stream.Collectors;
 import org.graalvm.collections.EconomicMap;
 import org.pkl.core.TestResults;
 import org.pkl.core.TestResults.Error;
@@ -38,11 +40,45 @@ import org.pkl.core.util.EconomicMaps;
 
 public final class JUnitReport implements TestReport {
 
+  private final String aggregateSuiteName;
+
+  public JUnitReport(String aggregateSuiteName) {
+    this.aggregateSuiteName = aggregateSuiteName;
+  }
+
+  public JUnitReport() {
+    this("");
+  }
+
   @Override
   public void report(TestResults results, Writer writer) throws IOException {
     writer.append(renderXML("    ", "1.0", buildSuite(results)));
   }
 
+  @Override
+  public void summarize(List<TestResults> allTestResults, Writer writer) throws IOException {
+    var totalTests = allTestResults.stream().collect(Collectors.summingLong(r -> r.totalTests()));
+    var totalFailures =
+        allTestResults.stream().collect(Collectors.summingLong(r -> r.totalFailures()));
+
+    assert aggregateSuiteName != null;
+
+    var attrs =
+        buildAttributes(
+            "name", aggregateSuiteName,
+            "tests", totalTests,
+            "failures", totalFailures);
+
+    var tests =
+        allTestResults.stream()
+            .map(r -> buildSuite(r))
+            .collect(Collectors.toCollection(ArrayList::new));
+
+    var suite = buildXmlElement("testsuites", attrs, tests.toArray(new VmDynamic[0]));
+
+    writer.append(renderXML("    ", "1.0", suite));
+  }
+
   private VmDynamic buildSuite(TestResults results) {
     if (results.error() != null) {
       var testCase = rootTestCase(results, results.error());

pkl-core/src/main/java/org/pkl/core/stdlib/test/report/SimpleReport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -57,6 +57,7 @@ public final class SimpleReport implements TestReport {
     writer.append(builder.toString());
   }
 
+  @Override
   public void summarize(List<TestResults> allTestResults, Writer writer) throws IOException {
     var totalTests = 0;
     var totalFailedTests = 0;

pkl-core/src/main/java/org/pkl/core/stdlib/test/report/TestReport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import java.io.IOException;
 import java.io.Writer;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
+import java.util.List;
 import org.pkl.core.PklBugException;
 import org.pkl.core.TestResults;
 import org.pkl.core.util.StringBuilderWriter;
@@ -28,7 +29,9 @@ public interface TestReport {
 
   void report(TestResults results, Writer writer) throws IOException;
 
-  default String report(TestResults results) {
+  void summarize(List<TestResults> allTestResults, Writer writer) throws IOException;
+
+  default String report(TestResults results) throws IOException {
     try {
       var builder = new StringBuilder();
       var writer = new StringBuilderWriter(builder);
@@ -44,4 +47,10 @@ public interface TestReport {
       report(results, writer);
     }
   }
+
+  default void summarizeToPath(List<TestResults> allTestResults, Path path) throws IOException {
+    try (var writer = new FileWriter(path.toFile(), StandardCharsets.UTF_8)) {
+      summarize(allTestResults, writer);
+    }
+  }
 }