[SPARK-3128][MLLIB] Use streaming test suite for StreamingLR

Refactored tests for streaming linear regression to use existing  streaming test utilities. Summary of changes:
- Made ``mllib`` depend on tests from ``streaming``
- Rewrote accuracy and convergence tests to use ``setupStreams`` and ``runStreams``
- Added new test for the accuracy of predictions generated by ``predictOnValue``

These tests should run faster, be easier to extend/maintain, and provide a reference for new tests.

mengxr tdas

Author: freeman <the.freeman.lab@gmail.com>

Closes #2037 from freeman-lab/streamingLR-predict-tests and squashes the following commits:

e851ca7 [freeman] Fixed long lines
50eb0bf [freeman] Refactored tests to use streaming test tools
32c43c2 [freeman] Added test for prediction

1 files changed, 3 insertions, 1 deletions

diff --git a/streaming/src/test/scala/org/apache/spark/streaming/TestSuiteBase.scala b/streaming/src/test/scala/org/apache/spark/streaming/TestSuiteBase.scala
index cc178fba12..f095da9cb5 100644
--- a/streaming/src/test/scala/org/apache/spark/streaming/TestSuiteBase.scala
+++ b/streaming/src/test/scala/org/apache/spark/streaming/TestSuiteBase.scala
@@ -242,7 +242,9 @@ trait TestSuiteBase extends FunSuite with BeforeAndAfter with Logging {
     logInfo("numBatches = " + numBatches + ", numExpectedOutput = " + numExpectedOutput)
 
     // Get the output buffer
-    val outputStream = ssc.graph.getOutputStreams.head.asInstanceOf[TestOutputStreamWithPartitions[V]]
+    val outputStream = ssc.graph.getOutputStreams.
+      filter(_.isInstanceOf[TestOutputStreamWithPartitions[_]]).
+      head.asInstanceOf[TestOutputStreamWithPartitions[V]]
     val output = outputStream.output
 
     try {