unittest addition

test/test_minirechner.c

@@ -25,4 +25,10 @@ void test_minitaschenrechner_float_plus_float(void)
     TEST_ASSERT_EQUAL(7.3, result);
 }
 
+void test_minitaschenrechner_minus1_plus_minus3(void)
+{
+    float result = addieren(-1, -3);
+    TEST_ASSERT_EQUAL(-4, result);
+}
+
 #endif // TEST