[BAEL-2996] Moved previous tests and added own implementation

libraries-2/src/test/java/com/baeldung/matrices/colt/DoubleMatrix2DUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.colt;
+package com.baeldung.matrices.colt;
 
 import cern.colt.matrix.DoubleFactory2D;
 import cern.colt.matrix.DoubleMatrix2D;

libraries-2/src/test/java/com/baeldung/matrices/ejml/SimpleMatrixUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.ejml;
+package com.baeldung.matrices.ejml;
 
 import org.ejml.simple.SimpleMatrix;
 import org.junit.jupiter.api.Test;

libraries-2/src/test/java/com/baeldung/matrices/homemade/MatrixUnitTest.java

@@ -0,0 +1,52 @@
+package com.baeldung.matrices.homemade;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class MatrixUnitTest {
+
+    @Test
+    void givenTwoMatrices_whenMultiply_thenMultiplicatedMatrix() {
+        double[][] firstMatrix = {
+          new double[]{1d, 5d},
+          new double[]{2d, 3d},
+          new double[]{1d, 7d}
+        };
+
+        double[][] secondMatrix = {
+          new double[]{1d, 2d, 3d, 7d},
+          new double[]{5d, 2d, 8d, 1d}
+        };
+
+        double[][] expected = {
+          new double[]{26d, 12d, 43d, 12d},
+          new double[]{17d, 10d, 30d, 17d},
+          new double[]{36d, 16d, 59d, 14d}
+        };
+
+        double[][] actual = multiplyMatrices(firstMatrix, secondMatrix);
+
+        assertThat(actual).isEqualTo(expected);
+    }
+
+    private double[][] multiplyMatrices(double[][] firstMatrix, double[][] secondMatrix) {
+        double[][] result = new double[firstMatrix.length][secondMatrix[0].length];
+
+        for (int row = 0; row < result.length; row++) {
+            for (int col = 0; col < result[row].length; col++) {
+                result[row][col] = multiplyMatricesCell(firstMatrix, secondMatrix, row, col);
+            }
+        }
+
+        return result;
+    }
+
+    private double multiplyMatricesCell(double[][] firstMatrix, double[][] secondMatrix, int row, int col) {
+        double cell = 0;
+        for (int i = 0; i < secondMatrix.length; i++) {
+            cell += firstMatrix[row][i] * secondMatrix[i][col];
+        }
+        return cell;
+    }
+}

libraries-2/src/test/java/com/baeldung/matrices/la4j/Basic2DMatrixUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.la4j;
+package com.baeldung.matrices.la4j;
 
 import org.junit.jupiter.api.Test;
 import org.la4j.Matrix;

libraries-2/src/test/java/com/baeldung/matrices/nd4j/INDArrayUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.nd4j;
+package com.baeldung.matrices.nd4j;
 
 import org.junit.jupiter.api.Test;
 import org.nd4j.linalg.api.ndarray.INDArray;