<Swing Dev> RFR: 8273043: [TEST_BUG] Automate NimbusJTreeSelTextColor.java [v2]

[Alexey Ivanov]

> Automated NimbusJTreeSelTextColor.java test which is added under [JDK-8271315](https://bugs.openjdk.java.net/browse/JDK-8271315).
> 
> It passes with the recent build of JDK 18.  
> It fails with JDK 18 build 7 where [JDK-8266510](https://bugs.openjdk.java.net/browse/JDK-8266510) is not fixed yet:
> 
> 
> Exception in thread "main" java.lang.RuntimeException: Unexpected color found: ff000000 at (4, 9);
> foreground: ffffffff; background: ff39698a - check image.png
>         at NimbusJTreeSelTextColor.checkColors(NimbusJTreeSelTextColor.java:106)
>         at NimbusJTreeSelTextColor.main(NimbusJTreeSelTextColor.java:70)
> 
> 
> The line is wrapped for readability. In this case the text is black instead of white.

Alexey Ivanov has updated the pull request incrementally with two additional commits since the last revision:

 - Mark the test headless
 - Paint JTree into BufferedImage

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5269/files
  - new: https://git.openjdk.java.net/jdk/pull/5269/files/76a173dd..4bf4e2e2

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5269&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5269&range=00-01

  Stats: 77 lines in 1 file changed: 32 ins; 20 del; 25 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5269.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5269/head:pull/5269

PR: https://git.openjdk.java.net/jdk/pull/5269