Fix flaky test in DeadLetterQueueTest

[LucaDai]

Fix Issue: https://github.com/GoogleCloudPlatform/DataflowTemplates/issues/2914 Similar fix before: https://github.com/GoogleCloudPlatform/DataflowTemplates/pull/1176

Root Cause

The flaky behavior was detected by NonDex when running com.google.cloud.teleport.v2.writer.DeadLetterQueueTest.

This test originally asserted partial JSON string containment using:

assertThat(dlq.rowContextToDlqElement(r1).getPayload())
    .contains(expectedDataWithSuccessfulConversion);

However, the generated JSON payloads within DeadLetterQueue#rowContextToDlqElement() are constructed using standard JSON serialization (via GSON / JSONObject), which does not guarantee deterministic field ordering. During serialization, additional metadata fields (e.g., metadata*) are dynamically inserted into a Map, and the iteration order of these keys may vary between JVM runs or environments.

As a result, the same logical payload could appear in different orders:

Run 1: {"timestamp_col":"1970-01-01T00:29:09.630376Z","new_quantity":"42"}
Run 2: {"_metadata_source_type":"mysql","timestamp_col":"1970-01-01T00:29:09.630376Z","new_quantity":"42","_metadata_table":"srcTable"}

Since the test relied on raw string matching, it failed whenever the key order changed, even though the underlying JSON content was semantically identical.

This issue is not specific to NonDex—it reflects an order-dependent assertion pattern that could also fail under normal JVM hash-seed variation.

Fix

Update the test to validate JSON semantics instead of raw string order: • Parse both the actual and expected payloads using JsonParser.parseString(...) and obtain JsonObject instances. • Assert equivalence of relevant fields (timestamp_col, new_quantity) instead of relying on the full serialized string. • Preserve the logic for verifying exception handling, but make the comparison robust to field order.

[gemini-code-assist[bot]]

Summary of Changes

Hello @LucaDai, I'm Gemini Code Assist[^1]! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a flaky test in DeadLetterQueueTest.java. The changes replace string contains assertions with JsonObject assertions to ensure accurate and reliable verification of the payload content, thus reducing the chance of false negatives.

Highlights

• Test Improvement: The PR modifies the DeadLetterQueueTest.java to improve the reliability of the test by using JsonObject for assertions instead of string contains.

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[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 55.33%. Comparing base (df0dbee) to head (46369c2). :warning: Report is 117 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2915      +/-   ##
============================================
+ Coverage     50.06%   55.33%   +5.27%     
+ Complexity     4973     1577    -3396     
============================================
  Files           967      462     -505     
  Lines         59329    25902   -33427     
  Branches       6448     2705    -3743     
============================================
- Hits          29703    14333   -15370     
+ Misses        27522    10701   -16821     
+ Partials       2104      868    -1236     

Components	Coverage Δ
spanner-templates	71.35% <ø> (+0.85%)	:arrow_up:
spanner-import-export	∅ <ø> (∅)
spanner-live-forward-migration	79.69% <ø> (ø)
spanner-live-reverse-replication	77.42% <ø> (ø)
spanner-bulk-migration	88.21% <ø> (ø)
see 524 files with indirect coverage changes

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