[SPARK-3418][MLlib] Matrix unit tests expanded with indexing and upda…

…ting

mllib/src/test/scala/org/apache/spark/mllib/linalg/MatricesSuite.scala

@@ -77,4 +77,39 @@ class MatricesSuite extends FunSuite {
 
     assert(!sparseMat.toArray.eq(sparseCopy.toArray))
   }
+
+  test("matrix indexing and updating") {
+    val m = 3
+    val n = 2
+    val allValues = Array(0.0, 1.0, 2.0, 3.0, 4.0, 0.0)
+
+    val denseMat = new DenseMatrix(m, n, allValues)
+
+    assert(denseMat(0, 1) == 3.0)
+    assert(denseMat(0, 1) == denseMat.values(3))
+    assert(denseMat(0, 1) == denseMat(3))
+    assert(denseMat(0, 0) == 0.0)
+
+    denseMat.update(0, 0, 10.0)
+    assert(denseMat(0, 0) == 10.0)
+    assert(denseMat.values(0) == 10.0)
+
+    val sparseValues = Array(1.0, 2.0, 3.0, 4.0)
+    val colIndices = Array(0, 2, 4)
+    val rowIndices = Array(1, 2, 0, 1)
+    val sparseMat = new SparseMatrix(m, n, colIndices, rowIndices, sparseValues)
+
+    assert(sparseMat(0, 1) == 3.0)
+    assert(sparseMat(0, 1) == denseMat.values(2))
+    assert(sparseMat(0, 1) == denseMat(2))
+    assert(sparseMat(0, 0) == 0.0)
+
+    intercept[IllegalArgumentException] {
+      sparseMat.update(0, 0, 10.0)
+    }
+
+    sparseMat.update(0, 1, 10.0)
+    assert(sparseMat(0, 1) == 10.0)
+    assert(sparseMat.values(2) == 10.0)
+  }
 }