Should I write integration test or unit test?

Question

Hi,

I have a function which saves photos(stored in database,app gives user option to save in a directory) to a given directory.Now, this was not working correctly.I just fixed it.Now, should I write unit test or integration test for the function?

Answer 1

Integration tests and unit tests have different scopes and purposes:

• Unit tests test small pieces of code (like a function) in isolation from the rest of the program, ideally covering all possible edge cases (like exceptions, null parameters, etc.)
• Integration tests test an entire application from a use case point of view. They can never cover all edge cases, but they can catch problems with the interaction between parts of the code and the glue code that joins them together which unit tests often miss

For a singe function, you can really only have a unit test, and you should. But you could also have an integration test that shows that when the user presses a certain button, a photo is written into the directory, and can be opened in the program as well.

Answer 2

Some people would call a test for a DAO an integration test; others would say it's a unit test.

Whatever you call it, I'd say you should have a unit test for all the DAO functionality and an integration test for the front-to-back behavior embodied in the use case that says "give the user the option to save to the file system." I'd have integration tests for both scenarios, since it sounds like both are possible in your system.

Answer 3

For your case, you want to write an integration test to cover the scenario you mention. I have a full post on this topic. However, here's a summarized version specific to your question:

In his book The Art of Unit Testing, Roy Osherove describes a key principle that a unit test must be “trustworthy”. On the surface, this seems fairly obvious. However, this underlying highlights some of the key differences between a unit test vs an integration test.

With a trustworthy test, you must be able trust the results 100% of the time. If the test fails, you want to be certain that the code is broken and must be fixed. You shouldn’t have to ask things like “Was the database down?”, “Was the connection string OK?”, “Was the stored procedure modified?”. By asking these questions, it shows that you aren't able to trust the results and you likely have a poorly designed “unit test”.

As your scenario describes a situation with similar multiple dependencies, you want to cover it with a integration test. Again, for more details, see my full post here as well.

Good luck!

Answer 4

I think it depends on the source of your problem. If the function itself may have some problems in different scenarios you can have unit tests to test this scenarios over your function. If integration of your function and other parts of your program may cause some problems you should think of an integration test. Sometimes a function like yours may need some external resources to do its job it's not a bad idea to have some unit tests to see what will happen if some of these resources are not available

Answer 5

• Integration tests help you to validate if your software is working properly.
• Unit tests help you to find why your software is breaking.

Unit tests to some extent also contribute to the first goal. Plus it has a couple of advantages:

• It's generally way cheaper to write and run a unit test with a much smaller scope.
• It's easier to get coverage for the combinatoric explosion of states of you components using unit tests than an integration test. Say you have a setup involving three components. Each of them has 3 different states. Then integration testing the entire setup would involve checking 3 * 3 * 3 = 27 conditions. Unit testing the individual components would require testing 3 + 3 + 3 = 9 conditions. (This is oversimplified, but you will hopefully see the point.)

Because of this, unit tests are generally more popular than integration tests. However, you really cannot do without integration tests. Integration tests should be the cornerstone used for acceptance of your software. Having unit tests only just proves that you have a bunch of stuff doing something. An integration test proves that you have working software.