Please create 3 different unit tests on the following methods in JAVA and explain how each unit test works. The tests should detect few bugs if found.

public Matrix multiplyWithScalar(double s, Matrix res) { if (res != null) { if ((res.getHeight() != height) || (res.getWidth() != width)) { return null; } // Scalar multiply for (int i = 1; i < height; i++) { for (int j = 1; j < width; j++) { res.matrix[i][j] = s * matrix[i][j]; } } } return res; }