Add junit-6-migration module: JUnit 5.14.4 vs 6.1.3, API diff and behaviour probes

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01YPgGH6aMbSLANL3E2HHmS6

junit-6-migration/README.md

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+# junit-6-migration
+
+Companion module for the ankurm.com article on **migrating from JUnit 5 to JUnit 6**. The same tests run on JUnit 5.14.4 and 6.1.3, and the two
+releases are compared jar against jar. Nothing here is copied from release notes: each file in `output/` was produced by running something.
+
+## Versions
+
+| Component | Version | Notes |
+|---|---|---|
+| JUnit (before) | `5.14.4` Jupiter / `1.14.4` Platform | last 5.x release on Maven Central at the time of writing |
+| JUnit (after) | `6.1.3` | Jupiter, Platform and Vintage all share this one number |
+| JUnit 4 | `4.13.2` | only for the Vintage check |
+| Java | build on `25`, `--release 17` | JUnit 6 jars need Java 17 |
+
+## Run
+
+```bash
+./scripts/run-all.sh
+```
+
+## Output
+
+| File | What it shows |
+|---|---|
+| `01-versions-and-baseline.txt` | version numbers and the Java level of each jar's class files |
+| `02-removed-api.txt` | public classes and members in 5.14.4 that are not in 6.1.3, and whether 5.14.4 had deprecated them |
+| `03-csv-behaviour-<version>.txt` | one set of `@CsvSource` and `@CsvFileSource` cases run on each version |
+| `04-vintage-junit4-<version>.txt` | a JUnit 4 test run through the Vintage engine on each version |
+| `05-old-apis-<version>.txt` | what the compiler says about three deprecated 5.x APIs on each version |
+| `06-fixed-apis-<version>.txt` | the replacements compile on both versions |
+
+`pom.xml` has two profiles, `junit5` and `junit6`, that change nothing but `junit.version`.