Github user sethah commented on a diff in the pull request:

    https://github.com/apache/spark/pull/10355#discussion_r57045359
  
    --- Diff: 
mllib/src/test/scala/org/apache/spark/ml/classification/RandomForestClassifierSuite.scala
 ---
    @@ -178,6 +179,34 @@ class RandomForestClassifierSuite extends 
SparkFunSuite with MLlibTestSparkConte
         assert(importances.toArray.forall(_ >= 0.0))
       }
     
    +  test("should support all NumericType labels") {
    +    val dfs = MLTestingUtils.genClassifDFWithNumericLabelCol(sqlContext, 
"label", "features")
    +
    +    val rf = new RandomForestClassifier().setFeaturesCol("features")
    +
    +    val expected = rf.setLabelCol("label")
    +      .fit(TreeTests.setMetadata(dfs(DoubleType), 2, "label"))
    +    dfs.keys.filter(_ != DoubleType).foreach { t =>
    +      TreeTests.checkEqual(expected,
    +        rf.setLabelCol("label").fit(TreeTests.setMetadata(dfs(t), 2, 
"label")))
    +    }
    +  }
    +
    +  test("shouldn't support non NumericType labels") {
    --- End diff --
    
    I still think the code duplication is a big concern. It might not be that 
hard to add some utility function that can clean this up. For example I was 
able to get this working:
    
    In _MLTestingUtils.scala_
    ```scala
    def checkRejectsNonNumericType(est: Predictor[_, _, _], sqlContext: 
SQLContext) = {
        val dfWithStringLabels =
          MLTestingUtils.generateDFWithStringLabelCol(sqlContext, 
est.getLabelCol, est.getFeaturesCol)
    
        val thrown = intercept[IllegalArgumentException] {
          est.fit(dfWithStringLabels)
        }
        assert(thrown.getMessage contains
          "Column label must be of type NumericType but was actually of type 
StringType")
      }
    ```
    
    Then in the actual test suites:
    ```scala
    test("shouldn't support non NumericType labels") {
        MLTestingUtils.checkRejectsNonNumericType(new RandomForestClassifier, 
sqlContext)
    }
    ```
    There will be some complication for some of the estimators like OneVsRest 
and IsotonicRegression (why doesn't it extend Predictor?) but I think it will 
be worth it to get this right since future estimators will have to implement 
this as well. It would be really nice to have something like we do for params 
where there is just a one-liner `ParamsSuite.checkParams(new 
RandomForestClassifier)`. For testing that all numeric types are supported, we 
could have a utility method that produces all actual and expected results, then 
check for equality inside the individual test suites, like:
    
    ```scala
    val models = MLTestingUtils.fitAllNumericTypes(new NaiveBayes, sqlContext)
        models.foreach { case (expected, actual) =>
          assert(expected.pi === actual.pi)
          assert(expected.theta === actual.theta)
        }
    ```
    
    I'm open to feedback on this, realizing it could be hard to generalize this 
for every case. 


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