Reinventing Some Wheels

A common practice in industry is test-driven development, whereby you write tests for code before you write the code itself. The tests themselves should be simple enough that they don’t need their own tests. For instance, a test might call some function one or more times, each time with different arguments, testing that the return values are expected. Let’s do just that.

Suppose that you’ve forgotten about ctype.h and so you’ve decided to implement your own versions of isalpha, isdigit, and isalnum as well as another function of your own, areupper. You’ve already declared prototypes for them in wheels/ctype.h, and you’ve even started to implement them in wheels/ctype.c but mostly in comments, temporarily returning false from most of them (so that the file will at least compile). You have, though, implemented isalpha already.

In wheels/check50.c, meanwhile, you’ve written a simplified implementation of check50. Notice how it calls test_isalpha, test_isdigit, test_isalnum, and test_areupper, all of which are declared in tests.h, and then, if all four of those functions work as expected, prints a single smiley face. Only one of those functions, test_isalpha, is actually implemented at the moment in wheels/tests.c. As you might expect, it tests isalpha, calling the function multiple times with different arguments, testing with assert that the return values are as expected. Per its manual page, if the input to assert is an expression that evaluates to false, assert will print an error message and abort the program (i.e., check50) immediately. If, though, the input to assert is an expression that evaluates to true, assert will do nothing, allowing execution continue.

Let’s test your (well, our) implementation of isalpha. In wheels/, execute

make check50


in order to compile the simplified version of check50 and, with it, ctype.c and tests.c. Then execute check50 and, with it, test_isalpha, with:

./check50


You should see a smiley face, because isalpha is not only implemented, it also passes all of the tests in test_isalpha!

Let’s implement the rest of the tests and the functions they test!

1. (5 points.) Complete the implementation of test_isdigit in wheels/tests.c in such a way that it tests isdigit, calling assert at least three times, each time with a different argument, testing that the function’s return value is as expected. Then, complete the implementation of isdigit itself, running check50 thereafter to ensure that you still see a smiley.
1. (5 points.) Complete the implementation of test_isalnum in wheels/tests.c in such a way that it tests isalnum, calling assert at least three times, each time with a different argument, testing that the function’s return value is as expected. Then, complete the implementation of isalnum itself, running check50 thereafter to ensure that you still see a smiley.
1. (5 points.) Complete the implementation of test_areupper in wheels/tests.c in such a way that it tests areupper, calling assert at least three times, each time with a different argument, testing that the function’s return value is as expected. Then, complete the implementation of areupper itself, running check50 thereafter to ensure that you still see a smiley.

Just keep in mind that that a smiley face means that your functions have passed all of your tests, but it doesn’t mean that all of your tests are correct!