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

src/test/c/test_taschenrechner.c

@@ -156,4 +156,18 @@ void test_exponentialFunction(void) {
     TEST_ASSERT_EQUAL_FLOAT(1.0, exponentialFunction(0.0));
 }
 
+// addition with two numbers
+void test_performOperation_Addition(void) {
+    // Arrange
+    int result;
+
+    // Act
+    result = performOperation(5, '+', 3);
+
+    // Assert
+    TEST_ASSERT_EQUAL_INT(8, result);
+}
+
+
+
 #endif // TEST