<Swing Dev> RFR: 8252825: Add automated test for fix done in JDK-8218479

Sun Sep 6 15:27:23 UTC 2020

Under JDK-8218479, fix was made to correct the rendering of JTextPane as the background color of JTextPane was similar
to Panel color, so it looked like the JTextPane has transparent background. No automated test was written to verify the
results. Current bug is to write the automated tests for the same.

The test fails without the fix done in JDK-8218479 and pass with the fix. I have run the tests multiple times in mach5.
Links in JBS.

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Commit messages:
 - 8252825: Add automated test for fix done in JDK-8218479

Changes: https://git.openjdk.java.net/jdk/pull/30/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=30&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252825
  Stats: 140 lines in 1 file changed: 140 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/30.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/30/head:pull/30

PR: https://git.openjdk.java.net/jdk/pull/30