add missed self-assignment check

A copy assignment operator must prevent that self-copy assignment ruins
the object state.

Issue: saebyn#28
Signed-off-by: Gluttton <gluttton@ukr.net>

Author: Gluttton

src/munkres-cpp/matrix.h

@@ -120,6 +120,10 @@ Matrix<T>::Matrix (size_t rows, size_t columns)
 template<class T>
 Matrix<T> & Matrix<T>::operator= (const Matrix<T> & other)
 {
+    if (this == & other) {
+        return *this;
+    }
+
     if (other.m_matrix != nullptr) {
         resize (other.m_rows, other.m_columns);
         std::copy (other.m_matrix[0], other.m_matrix[0] + m_rows * m_columns, m_matrix[0]);

tests/matrix_test.cpp

@@ -127,6 +127,22 @@ TEST_F (MatrixTest, operatorAssignment_0x0_Success)
 
 
 
+TEST_F (MatrixTest, operatorAssignment_1x1_self_Success)
+{
+    // Arrange.
+    munkres_cpp::Matrix<double> etalon_matrix {
+        {1.1}
+    };
+
+    // Act.
+    etalon_matrix = etalon_matrix;
+
+    // Assert.
+    EXPECT_EQ (1.1, etalon_matrix (0, 0) );
+}
+
+
+
 TEST_F (MatrixTest, operatorAssignment_3x3_Success)
 {
     // Arrange.