Added all the four unittest back in the test_calculator.c file (test_performOperation_Multiplication, test_performOperation_Addition, test_performOperation_Subtraction and test_performOperation_Division)

src/test/c/test_taschenrechner.c

@@ -156,4 +156,40 @@ void test_exponentialFunction(void) {
     TEST_ASSERT_EQUAL_FLOAT(1.0, exponentialFunction(0.0));
 }
 
+// Test case for subtraction
+void test_performOperation_Subtraction(void) {
+    // Arrange
+    int result;
+
+    // Act
+    result = performOperation(10, '-', 3);
+
+    // Assert
+    TEST_ASSERT_EQUAL_INT(7, result);
+}
+
+// Test case for multiplication
+void test_performOperation_Multiplication(void) {
+    // Arrange
+    int result;
+
+    // Act
+    result = performOperation(4, '*', 6);
+
+    // Assert
+    TEST_ASSERT_EQUAL_INT(24, result);
+}
+
+// Test case for division
+void test_performOperation_Division(void) {
+    // Arrange
+    int result;
+
+    // Act
+    result = performOperation(8, '/', 2);
+
+    // Assert
+    TEST_ASSERT_EQUAL_INT(4, result);
+}
+
 #endif // TEST