Test failures with OpenJDK 21

[jamesjer]

Attempting to build flexmark-java with OpenJDK 21 on an x86_64 Fedora 40 machine leads to test failures. OpenJDK 17 and earlier work. This is the first test failure:

[INFO] Running com.vladsch.flexmark.ext.abbreviation.ComboAbbreviationSpecTest
[ERROR] Tests run: 22, Failures: 2, Errors: 0, Skipped: 0, Time elapsed: 0.085 s <<< FAILURE! -- in com.vladsch.flexmark.ext.abbreviation.ComboAbbreviationSpecTest
[ERROR] com.vladsch.flexmark.ext.abbreviation.ComboAbbreviationSpecTest.testSpecExample[Full Spec] -- Time elapsed: 0.055 s <<< FAILURE!
org.junit.ComparisonFailure: 
file:///builddir/build/BUILD/flexmark-java-0.64.6-build/flexmark-java-0.64.6/flexmark-ext-abbreviation/src/test/resources/ext_abbreviation_ast_spec.md expected:<...ca">U.S.A.</abbr>, ([<abbr title="États-Unis d'Amérique">É.U.</abbr> or É.-U. d&rsquo;A. in French).</p>
<p>And here we have a <abbr title="Compact Disk">CD</abbr>, some CDs, and some other <abbr title="Compact Disk">CD</abbr>&rsquo;s.</p>
<p>Let&rsquo;s transfert documents through <abbr title="Transmission Control Protocol">TCP</abbr>/<abbr title="Internet Protocol">IP</abbr>, using <abbr title="Transmission Control Protocol">TCP</abbr> packets.</p>
.
Document[0, 535]
  Paragraph[0, 38] isTrailingBlankLine
    TextBase[0, 37] chars:[0, 37, "Some  … TML4."]
      Text[0, 16] chars:[0, 16, "Some  … bout "]
      Abbreviation[16, 20] chars:[16, 20, "HTML"]
      Text[20, 22] chars:[20, 22, ", "]
      Abbreviation[22, 26] chars:[22, 26, "SGML"]
      Text[26, 31] chars:[26, 31, " and "]
      Abbreviation[31, 36] chars:[31, 36, "HTML4"]
      Text[36, 37] chars:[36, 37, "."]
  Paragraph[39, 100] isTrailingBlankLine
    Text[39, 42] chars:[39, 42, "Let"]
    TypographicSmarts[42, 43] typographic: &rsquo; 
    TextBase[43, 84] chars:[43, 84, "s tal … -U. d"]
      Text[43, 60] chars:[43, 60, "s tal …  the "]
      Abbreviation[60, 66] chars:[60, 66, "U.S.A."]
      Text[66, 69] chars:[66, 69, ", ("]
      Abbreviation[69, 73] chars:[69, 73, "É.U."]
      Text[73, 84] chars:[73, 84, " or É] … -U. d"]
    Typog...> but was:<...ca">U.S.A.</abbr>, ([É.U. or É.-U. d&rsquo;A. in French).</p>
<p>And here we have a <abbr title="Compact Disk">CD</abbr>, some CDs, and some other <abbr title="Compact Disk">CD</abbr>&rsquo;s.</p>
<p>Let&rsquo;s transfert documents through <abbr title="Transmission Control Protocol">TCP</abbr>/<abbr title="Internet Protocol">IP</abbr>, using <abbr title="Transmission Control Protocol">TCP</abbr> packets.</p>
.
Document[0, 535]
  Paragraph[0, 38] isTrailingBlankLine
    TextBase[0, 37] chars:[0, 37, "Some  … TML4."]
      Text[0, 16] chars:[0, 16, "Some  … bout "]
      Abbreviation[16, 20] chars:[16, 20, "HTML"]
      Text[20, 22] chars:[20, 22, ", "]
      Abbreviation[22, 26] chars:[22, 26, "SGML"]
      Text[26, 31] chars:[26, 31, " and "]
      Abbreviation[31, 36] chars:[31, 36, "HTML4"]
      Text[36, 37] chars:[36, 37, "."]
  Paragraph[39, 100] isTrailingBlankLine
    Text[39, 42] chars:[39, 42, "Let"]
    TypographicSmarts[42, 43] typographic: &rsquo; 
    TextBase[43, 84] chars:[43, 84, "s tal … -U. d"]
      Text[43, 60] chars:[43, 60, "s tal …  the "]
      Abbreviation[60, 66] chars:[60, 66, "U.S.A."]
      Text[66, 84] chars:[66, 84, ", (É.] … -U. d"]
    Typog...>
	at org.junit.Assert.assertEquals(Assert.java:117)
	at com.vladsch.flexmark.test.util.FullSpecTestCase.testSpecExample(FullSpecTestCase.java:48)
	at com.vladsch.flexmark.test.util.ComboSpecTestCase.testSpecExample(ComboSpecTestCase.java:100)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:61)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.rules.ExpectedException$ExpectedExceptionStatement.evaluate(ExpectedException.java:258)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
	at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
	at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
	at org.junit.runners.Suite.runChild(Suite.java:128)
	at org.junit.runners.Suite.runChild(Suite.java:27)
	at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
	at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
	at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:316)
	at org.apache.maven.surefire.junit4.JUnit4Provider.executeWithRerun(JUnit4Provider.java:240)
	at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:214)
	at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:155)
	at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:385)
	at org.apache.maven.surefire.booter.ForkedBooter.execute(ForkedBooter.java:162)
	at org.apache.maven.surefire.booter.ForkedBooter.run(ForkedBooter.java:507)
	at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:495)

[jamesjer]

Any thoughts on how to debug this issue would be very welcome, as Fedora is moving toward dropping all JDKs prior to OpenJDK 21.