skill(apm-integrations): clarify + consolidate Groovy-vs-Java test DSL rule

.agents/skills/apm-integrations/SKILL.md

@@ -43,16 +43,13 @@ pattern before writing new code. Use it as a template.
 
 ## Step 4 – Set up the module
 
-1. Create directory: `dd-java-agent/instrumentation/$framework/$framework-$minVersion/`
-2. Under it, create the standard Maven source layout:
-   - `src/main/java/` — instrumentation code
-   - `src/test/groovy/` — Groovy/Spock instrumentation tests (see Step 9.1)
-3. Create `build.gradle` with:
+1. Create directory: `dd-java-agent/instrumentation/$framework/$framework-$minVersion/`, with the standard Maven source layout under it (`src/main/java/` for instrumentation code; test source dir per Step 9.1)
+2. Create `build.gradle` with:
    - `compileOnly` dependencies for the target framework
    - `testImplementation` dependencies for tests
    - `muzzle { pass { } }` directives (see Step 9.2)
-4. Register the new module in `settings.gradle.kts` in **alphabetical order**
-5. Register all integration names in `metadata/supported-configurations.json` — **read [Supported Configurations](references/supported-configurations.md)** for the exact key shapes and CI checks involved. Declaring several names (`super("a", "b")`) means one entry each.
+3. Register the new module in `settings.gradle.kts` in **alphabetical order**
+4. Register all integration names in `metadata/supported-configurations.json` — **read [Supported Configurations](references/supported-configurations.md)** for the exact key shapes and CI checks involved. Declaring several names (`super("a", "b")`) means one entry each.
 
 **See [Naming Conventions](references/naming-conventions.md) — module directory name must end with a version or an allowed suffix (`-common`, `-stubs`, `-iast`). Java filename and `public class` name MUST match character-for-character including acronym casing (CRITICAL — see § "Java naming consistency").**
 
@@ -93,7 +90,7 @@ Cover all mandatory test types:
 
 ### 1. Instrumentation test (mandatory)
 
-**Read [Writing Tests](references/tests.md).** Instrumentation tests are Groovy/Spock (`src/test/groovy/`) — add the `tag: override groovy enforcement` label to suppress the `Enforce Groovy Migration` CI check (which blocks new `.groovy` files by default — instrumentation tests are intentionally Groovy/Spock). Must cover error/exception scenarios. When adding new integration names, register them per [Supported Configurations](references/supported-configurations.md). When `compileOnly` and `testImplementation` use different versions, comment the specific class that requires the higher version. Include sibling version modules as `testImplementation` dependencies for mutual-exclusion tests.
+**Read [Writing Tests](references/tests.md) — it defines the Groovy-vs-Java DSL rule; follow it before creating any test files.** Adding new `.groovy` files to a PR triggers the `Enforce Groovy Migration` CI check — add the `tag: override groovy enforcement` label to suppress it. Must cover error/exception scenarios. When adding new integration names, register them per [Supported Configurations](references/supported-configurations.md). When `compileOnly` and `testImplementation` use different versions, comment the specific class that requires the higher version. Include sibling version modules as `testImplementation` dependencies for mutual-exclusion tests.
 
 ### 2. Muzzle directives (mandatory)
 

.agents/skills/apm-integrations/references/tests.md

@@ -4,7 +4,7 @@
 
 ## 1. Instrumentation test (mandatory)
 
-**Write Groovy/Spock tests for instrumentation tests** (per `AGENTS.md`: "Only use Groovy / Spock tests for instrumentation and smoke tests"). Full Java instrumentation test support is not yet available. Adding new `.groovy` files to a PR will trigger the `Enforce Groovy Migration` bot — add the `tag: override groovy enforcement` label to bypass it.
+**Write Groovy/Spock tests for instrumentation tests** (per `AGENTS.md`: "Only use Groovy / Spock tests for instrumentation and smoke tests"). This is unconditional — including for modules whose existing siblings happen to use Java/JUnit — an existing Java-DSL sibling is NOT license to add more Java tests; do not migrate a Groovy family to Java either. Confirm what the family is on with `ls src/test/` on the module's master version and its version-siblings (e.g. `jedis-1.4/`, `jedis-4.0/` for `jedis-3.0`) before writing tests. This file also shows Java `AbstractInstrumentationTest` examples below; those exist ONLY to illustrate style rules (no-banner-comments, error-path coverage) for modules that are ALREADY on the Java/JUnit DSL — they are NOT a license to introduce Java into a Groovy family. Introducing a `src/test/java/**` test into a module whose siblings are `src/test/groovy/**` diverges from master's style and can trip the Java DSL's stricter tag matcher, producing spurious CI failures that are NOT instrumentation defects. Adding new `.groovy` files to a PR will trigger the `Enforce Groovy Migration` bot — add the `tag: override groovy enforcement` label to bypass it.
 
 - Groovy/Spock test class in `src/test/groovy/datadog/trace/instrumentation/<framework>/`
 - Verify: spans created, tags set, errors propagated, resource names correct
@@ -129,9 +129,10 @@ Common libraries where this split matters: Reactor, Netty, gRPC, Kafka clients (
 
 Do NOT insert banner-style separator comments (e.g. `// --------- Successful completion ---------`) inside test files to group related test methods. Banner comments have unclear scope, don't render usefully in IDEs, and add review burden without a benefit that justifies the noise.
 
-**If a group of related tests warrants its own heading**, extract them into a separate test class with a focused class-level Javadoc:
+**If a group of related tests warrants its own heading**, extract them into a separate test class with a focused class-level Javadoc.
 
 ```java
+// Java example, style only — same rule applies to Groovy/Spock (see DSL rule above)
 // ❌ Banner comments
 class RxJava3ResultExtensionTest extends AbstractInstrumentationTest {
   // ---------------------------------------------------------------------------