Isolate conformance test workers to fix parallel-run flakiness

Enabling parallel test forks let concurrent conformance battles collide
on the shared compat-test/work directory, intermittently corrupting
TurnBoundaryConformanceTest (and other conformance tests) under
./gradlew clean build. Each Gradle test worker now gets its own
COMPAT_WORK_DIR, and the test task depends on the harness's own jars
being built first rather than racing them.

Verified with three consecutive `./gradlew clean build` runs: 0
failures across all 28 test result files.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TtiGhPTwQoK8CQkf7yffVm

Author: flemming-n-larsen

build.gradle.kts

@@ -1,10 +1,23 @@
+import org.gradle.api.tasks.testing.Test
+
 plugins {
     java
     alias(libs.plugins.kotlin.jvm) apply false
 }
 
+val testForks = providers.gradleProperty("test.maxParallelForks")
+    .map(String::toInt)
+    .orElse(Runtime.getRuntime().availableProcessors().coerceAtMost(8).coerceAtLeast(1))
+
 allprojects {
     repositories {
         mavenCentral()
     }
 }
+
+subprojects {
+    tasks.withType<Test>().configureEach {
+        // Test forks are isolated JVMs. Harness-backed tests assign each fork its own work dir.
+        maxParallelForks = testForks.get()
+    }
+}

compat-test/compat_test.py

@@ -112,7 +112,7 @@ def local_bot_api_jar():
 STATE_FILE = BASE_DIR / "test_progress.json"
 REPORT_FILE = BASE_DIR / "compatibility_report.md"
 ERRORS_DIR = BASE_DIR / "errors"
-WORK_DIR = BASE_DIR / "work"
+WORK_DIR = Path(os.environ.get("COMPAT_WORK_DIR", BASE_DIR / "work"))
 
 RC_WORKER = BASE_DIR / "RcBattleWorker.java"
 TR_WORKER = BASE_DIR / "TrBattleWorker.java"

conformance-test/build.gradle.kts

@@ -34,6 +34,9 @@ java {
 // each engine runs in its own process (ARCH-003).
 tasks {
     test {
+        // The harness consumes these files directly rather than resolving them as Gradle dependencies.
+        dependsOn(":robocode-api:jar", ":robots-wrapper:fatJar")
+
         useJUnitPlatform()
         testLogging {
             events("failed", "skipped")

conformance-test/src/test/java/dev/robocode/tankroyale/bridge/conformance/ConformanceHarness.java

@@ -26,6 +26,10 @@ final class ConformanceHarness {
 
     private static final Path REPO_ROOT = locateRepoRoot();
     private static final Path HARNESS = REPO_ROOT.resolve("compat-test").resolve("compat_test.py");
+    private static final Path WORK_ROOT = REPO_ROOT.resolve("compat-test").resolve("work");
+    private static final Path WORK_DIR = WORK_ROOT.resolve(
+            "gradle-worker-" + System.getProperty("org.gradle.test.worker", "1")
+                    + "-" + ProcessHandle.current().pid());
 
     private final String python;
     private final Path robocodeHome;
@@ -121,10 +125,7 @@ BattleOutcome runTeam(Engine engine, String teamClass, Path source) {
                 "--robocode-home", robocodeHome.toString()));
 
         try {
-            Process process = new ProcessBuilder(command)
-                    .directory(HARNESS.getParent().toFile())
-                    .redirectErrorStream(false)
-                    .start();
+            Process process = startHarness(command);
 
             AtomicReference<String> out = new AtomicReference<>("");
             AtomicReference<String> err = new AtomicReference<>("");
@@ -179,10 +180,7 @@ private BattleOutcome run(Engine engine, String robotClass, Path source, String
         }
 
         try {
-            Process process = new ProcessBuilder(command)
-                    .directory(HARNESS.getParent().toFile())
-                    .redirectErrorStream(false)
-                    .start();
+            Process process = startHarness(command);
 
             // Both pipes are drained concurrently, and the wait comes before either is
             // read. Draining one to EOF first deadlocks as soon as the harness writes more
@@ -222,6 +220,15 @@ private static BattleOutcome failed(String detail) {
         return new BattleOutcome(false, List.of(), List.of(), null, detail);
     }
 
+    /** Starts a harness process with workspace isolation for this Gradle test worker. */
+    private static Process startHarness(List<String> command) throws IOException {
+        ProcessBuilder builder = new ProcessBuilder(command)
+                .directory(HARNESS.getParent().toFile())
+                .redirectErrorStream(false);
+        builder.environment().put("COMPAT_WORK_DIR", WORK_DIR.toString());
+        return builder.start();
+    }
+
     /**
      * The harness prints its result as a single JSON object on the last non-blank line;
      * anything before it is progress output.