Added unittest for the case in to check the performOperation function's ability to perform multiplication. Includes arranging operands, performing multiplication, and asserting the expected result.

src/test/c/test_taschenrechner.c

@@ -180,4 +180,16 @@ void test_performOperation_Subtraction(void) {
     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);
+}
+
 #endif // TEST