add unit test for changes to change training related params like loss to only be validated during fitting phase

Author: asarb

mllib/src/main/scala/org/apache/spark/ml/regression/LinearRegression.scala

@@ -115,7 +115,6 @@ private[regression] trait LinearRegressionParams extends PredictorParams
           "normal solver, please change solver to auto or l-bfgs.")
         require($(elasticNetParam) == 0.0, "LinearRegression with huber loss only supports " +
           s"L2 regularization, but got elasticNetParam = $getElasticNetParam.")
-
       }
     }
     super.validateAndTransformSchema(schema, fitting, featuresDataType)

mllib/src/test/scala/org/apache/spark/ml/regression/LinearRegressionSuite.scala

@@ -187,6 +187,18 @@ class LinearRegressionSuite extends MLTest with DefaultReadWriteTest with PMMLRe
     assert(model.numFeatures === numFeatures)
   }
 
+  test("linear regression: can transform data with LinearRegressionModel") {
+    withClue("training related params like loss are only validated during fitting phase") {
+      val original = new LinearRegression().fit(datasetWithDenseFeature)
+
+      val deserialized = new LinearRegressionModel(uid = original.uid,
+        coefficients = original.coefficients,
+        intercept = original.intercept)
+      val output = deserialized.transform(datasetWithDenseFeature)
+      assert(output.collect().size > 0) // simple assertion to ensure no exception thrown
+    }
+  }
+
   test("linear regression: illegal params") {
     withClue("LinearRegression with huber loss only supports L2 regularization") {
       intercept[IllegalArgumentException] {