[SPARK-23882][Core] UTF8StringSuite.writeToOutputStreamUnderflow() is not expected to be supported

[kiszk]

What changes were proposed in this pull request?

This PR excludes an existing UT writeToOutputStreamUnderflow() in UTF8StringSuite.

As discussed here, the behavior of this test looks surprising. This test seems to access metadata area of the JVM object where is reserved by Platform.BYTE_ARRAY_OFFSET.

This test is introduced thru #16089 by @NathanHowell. More specifically, the commit Improve test coverage of UTFString.write introduced this UT. However, I cannot find any discussion about this UT.

I think that it would be good to exclude this UT.

  public void writeToOutputStreamUnderflow() throws IOException {
    // offset underflow is apparently supported?
    final ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    final byte[] test = "01234567".getBytes(StandardCharsets.UTF_8);

    for (int i = 1; i <= Platform.BYTE_ARRAY_OFFSET; ++i) {
      new UTF8String(
        new ByteArrayMemoryBlock(test, Platform.BYTE_ARRAY_OFFSET - i, test.length + i))
          .writeTo(outputStream);
      final ByteBuffer buffer = ByteBuffer.wrap(outputStream.toByteArray(), i, test.length);
      assertEquals("01234567", StandardCharsets.UTF_8.decode(buffer).toString());
      outputStream.reset();
    }
  }

How was this patch tested?

Existing UTs

[kiszk]

cc @NathanHowell, @cloud-fan, @viirya

[SparkQA]

Test build #88978 has finished for PR 20995 at commit b47b861.

• This patch fails to build.
• This patch merges cleanly.
• This patch adds no public classes.

[hvanhovell]

@kiszk let's just remove the test. It should have never been added in the first place.

[SparkQA]

Test build #88979 has finished for PR 20995 at commit 04e9d5f.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #88984 has finished for PR 20995 at commit d2dc70f.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[hvanhovell]

LGTM - merging to master. Thanks!

[ueshin]

Seems like this broke lint-java.

[ERROR] src/test/java/org/apache/spark/unsafe/types/UTF8StringSuite.java:[28,8] (imports) UnusedImports: Unused import - org.apache.spark.unsafe.Platform.

@kiszk Could you fix it? Thanks!

[kiszk]

@ueshin, sorry for my mistake again. I will fix this at #20871

[kiszk]

@ueshin Finally, I found better PR to fix this issue.