add-gc-test

You are helping add an integration test to `TestGCMetrics.java` for new GC collector support. ## Changes Introducing New GC Collectors ```diff !`git diff master -- src/main/resources/org/datadog/jmxfetch/new-gc-default-jmx-metrics.yaml 2>/dev/null || git diff HEAD~1 -- src/main/resources/org/datadog/jmxfetch/new-gc-default-jmx-metrics.yaml 2>/dev/null || echo "(no diff found — check the branch or commit manually)"` ``` $ARGUMENTS ## Your Task 1. **Read** `src/main/resources/org/datadog/jmxfetch/new-gc-default-jmx-metrics.yaml` — identify which new collector `name:` entries were added and what `alias:` metrics they map to. 2. **Read** `src/test/java/org/datadog/jmxfetch/TestGCMetrics.java` — understand existing test patterns and pick up on the `startAndGetMetrics` helper and both `assertGCMetric` overloads. 3. **Read** `src/test/java/org/datadog/jmxfetch/util/server/JDKImage.java` — confirm available JDK image constants (`JDK_8`, `JDK_11`, `JDK_11_OPENJ9`, `JDK_17`, `JDK_21`). 4. **Add** a new `@Test` method to `TestGCMetrics.java` following the patterns below. ## Patterns ### Standard GC with paired minor + major collectors ```java @Test public void testDefaultNewGCMetricsUse<GCName>() throws IOException { try (final MisbehavingJMXServer server = new MisbehavingJMXServer.Builder().withJDKImage( <JDK_IMAGE>).appendJavaOpts("<-XX:+UseXxxGC>").build()) { final List<Map<String, Object>> actualMetrics = startAndGetMetrics(server, true); assertThat(actualMetrics, hasSize(13)); assertGCMetric(actualMetrics, "jvm.gc.minor_collection_count", "<YoungCollectorName>", "counter"); assertGCMetric(actualMetrics, "jvm.gc.minor_collection_time", "<YoungCollectorName>", "counter"); assertGCMetric(actualMetrics, "jvm.gc.major_collection_count", "<OldCollectorName>", "counter"); assertGCMetric(actualMetrics, "jvm.gc.major_collection_time", "<OldCollectorName>", "counter"); } } ``` ### GC with more than 2 active collectors (e.g., Generational ZGC with 4) Use the `assertGCMetric(actualMetrics, metric, List<String> gcGenerations)` overload: ```java assertGCMetric(actualMetrics, "jvm.gc.major_collection_count", Arrays.asList("<Collector1>", "<Collector2>")); ``` ### Metric count formula `hasSize(9 + N*2)` where N = number of distinct GC collector names active with that JVM flag. - 9 = base JVM metrics (heap, threads, classes, etc.) emitted when `collect_default_jvm_metrics: true` + `new_gc_metrics: true` - Each collector emits 2 metrics: count + time - Examples: 2 collectors → `hasSize(13)`, 4 collectors → `hasSize(17)` ### JDK image guidance | GC flag | JDK image | |---|---| | `-XX:+UseSerialGC`, `-XX:+UseParallelGC`, `-XX:+UseConcMarkSweepGC`, `-XX:+UseG1GC` | `JDK_11` | | `-XX:+UseZGC` (non-generational) | `JDK_17` | | `-XX:+UseZGC -XX:+ZGenerational` | `JDK_21` | | `-XX:+UseShenandoahGC` | `JDK_17` or `JDK_21` | | `-Xgcpolicy:gencon`, `-Xgcpolicy:balanced` | `JDK_11_OPENJ9` | | GraalVM Native | no `MisbehavingJMXServer` support yet — note this limitation | ### Metric alias mapping Look at the alias values in the YAML diff to determine which metric names to assert: - `jvm.gc.minor_collection_count` / `jvm.gc.minor_collection_time` — young gen collectors - `jvm.gc.major_collection_count` / `jvm.gc.major_collection_time` — old gen collectors - Custom aliases (e.g., `jvm.gc.zgc_cycles_collection_count`) — assert those directly ## Code Style Requirements - 4-space indentation, no tabs - Lines ≤ 100 characters — wrap `appendJavaOpts(...)` onto a second line if needed - Method name in camelCase: `testDefaultNewGCMetrics<Descriptive Suffix>` - No Javadoc required on test methods - Imports: add any missing ones in the correct group (static → special → third-party → java → javax) ## After Writing the Test Run Checkstyle to verify formatting: ```bash ./mvnw checkstyle:check 2>&1 | grep -E "ERROR|WARNING|BUILD" | tail -20 ``` If the new GC requires a JDK image not in `JDKImage.java`, note that it needs to be added there first.