Github user srowen commented on a diff in the pull request: https://github.com/apache/spark/pull/14551#discussion_r74005685 --- Diff: core/src/test/scala/org/apache/spark/util/UtilsSuite.scala --- @@ -874,4 +874,38 @@ class UtilsSuite extends SparkFunSuite with ResetSystemProperties with Logging { } } } + + test("chi square test of randomizeInPlace") { + // Parameters + val arraySize = 10 + val numTrials = 1000 + val threshold = 0.05 + val seed = 1L + + // results[i][j]: how many times Utils.randomize moves an element from position j to position i + val results: Array[Array[Long]] = Array.ofDim(arraySize, arraySize) + + // This must be seeded because even a fair random process will fail this test with + // probability equal to the value of `threshold`, which is inconvenient for a unit test. + val rand = new java.util.Random(seed) + val range = 0 until arraySize + + for { + _ <- 0 until numTrials + trial = Utils.randomizeInPlace(range.toArray, rand) --- End diff -- I think this ends up being a little hard to grok. Just do two nested loops
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