[BUG] org.opensearch.search.nested.SimpleNestedExplainIT.testExplainMultipleDocs is flaky

[reta]

Describe the bug

The test case org.opensearch.search.nested.SimpleNestedExplainIT.testExplainMultipleDocs is flaky:

org.opensearch.search.nested.SimpleNestedExplainIT.testExplainMultipleDocs


java.lang.AssertionError: expected:<0.36464313 = Score based on 2 child docs in range from 0 to 1, using score mode Total
  0.18232156 = weight(nested1.n_field1:n_value1 in 0) [PerFieldSimilarity], result of:
    0.18232156 = score(freq=1.0), computed as boost * idf * tf from:
      2.2 = boost
      0.18232156 = idf, computed as log(1 + (N - n + 0.5) / (n + 0.5)) from:
        2 = n, number of documents containing term
        2 = N, total number of documents with field
      0.45454544 = tf, computed as freq / (freq + k1 * (1 - b + b * dl / avgdl)) from:
        1.0 = freq, occurrences of term within document
        1.2 = k1, term saturation parameter
        0.75 = b, length normalization parameter
        1.0 = dl, length of field
        1.0 = avgdl, average length of field
> but was:<0.36464313 = Score based on 2 child docs in range from 14 to 15, using score mode Total
  0.18232156 = weight(nested1.n_field1:n_value1 in 14) [PerFieldSimilarity], result of:
    0.18232156 = score(freq=1.0), computed as boost * idf * tf from:
      2.2 = boost
      0.18232156 = idf, computed as log(1 + (N - n + 0.5) / (n + 0.5)) from:
        2 = n, number of documents containing term
        2 = N, total number of documents with field
      0.45454544 = tf, computed as freq / (freq + k1 * (1 - b + b * dl / avgdl)) from:
        1.0 = freq, occurrences of term within document
        1.2 = k1, term saturation parameter
        0.75 = b, length normalization parameter
        1.0 = dl, length of field
        1.0 = avgdl, average length of field
>

Related component

Search

To Reproduce

./gradlew ':server:internalClusterTest' --tests "org.opensearch.search.nested.SimpleNestedExplainIT.testExplainMultipleDocs" -Dtests.seed=52C9CA95BCB30A28 

Expected behavior

The test must always pass

Additional Details

Plugins
Standard

Screenshots
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Host/Environment (please complete the following information):

• CI

Additional context

• https://build.ci.opensearch.org/job/gradle-check/33757/testReport/junit/org.opensearch.search.nested/SimpleNestedExplainIT/testExplainMultipleDocs/

[peternied]

[Triage - attendees 1 2 3 4 5 6]
@reta Thanks for filing, we would be happy to review a pull request