My Testing Experience

Before my days of automated testing…

I wrote only solid code!

There’s no time for tests!

So what brought me to automated testing?

My code isn’t solid!

Everyday, I’m struggling!

Automated Testing Benefits

• Discover problems upfront
• Eases refactoring
• Tests are documentation
• Helps identify bad design
• Reduce regression bugs
• Reduce code change fears!

Writing Proper Tests

• A test should have clear and simple goals
• A test should be deterministic
• A test should test the right thing

Make Them With Simple Goals

Make Them Deterministic

Make Them Test The Right Thing

How to Start?

• Focus on testing the most important parts of your code.
• When you encounter a bug, write a test for it.
• When you’re unsure of what happening in code, write a test to explain it.
• When short on time, work more on end-to-end tests.
• When you have plenty of time, work more on unit tests.
• When you have free time, write any test.

Simple Example: Fibonacci in C++

Code:

int fib(int n) {
  if (n <= 0) { return 0; }
  else if (n == 1) { return 1; }
  else { return fib(n-2) + fib(n-1); }
}
void main() {
  cout << fib(5) << endl;
}

Test:

void testFib() {
  // given
  int n = 6;
  // when
  int x = fib(n);
  // then
  assert(x, 8);
}

Hard to Test Example

public class EntityController {

  IRepo repo = new EntityRepo(...);

  public Entity find(int id) {
    Date d = Date.now();
    if (d.getTime() % 60000 >= 30000) {
      return repo.getEntity(id, d);
    } else {
      return null;
    }
  }

}

Less Hard to Test Example

public class EntityController {

  private IRepo repo;

  // we can perform dependency injection
  public IRepo setRepo(IRepo r) {
    repo = r;
  }

  // we can maintain backwards compatibility
  public Entity find(int id) {
    return find(id, Date.now());
  }

  // ... and still test deterministically
  public Entity find(int id, Date d) {
    if (d.getTime() % 60000 >= 30000) {
      return repo.getEntity(id, d);
    } else {
      return null;
    }
  }
}

How I Feel About Tests Now

• I cannot live without some form of automated testing.
• Testing consumes a lot of time. Automating testing consumes a lot of time upfront, but pays off in the long run.
• It’s hard to write good tests.
• Automated tests are useful until you discover that you’re doing it all wrong.
• You must fix your tests as soon as they break.
• Don’t stop writing automated tests until you have confidence in your test suite.
• Make sure the tests run in a reasonable amount of time.

Conclusion?

Questions?

(Ask now)

These slides have been open-sourced and are available @ https://github.com/pcting/slides_testxp