RFR: 8377244: Update ModuleReaderTest to JUnit prior to making changes

[David Beaumont]

Updated legacy TestNG asserts to JUnit and added useful context to help debugging when assertions fail.

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Commit messages:
 - Update test to JUnit

Changes: https://git.openjdk.org/jdk/pull/29588/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29588&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377244
  Stats: 105 lines in 1 file changed: 6 ins; 55 del; 44 mod
  Patch: https://git.openjdk.org/jdk/pull/29588.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29588/head:pull/29588

PR: https://git.openjdk.org/jdk/pull/29588