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GNU Smalltalk User's Guide

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2.7.4.3 How do you test for expected results?

If you're testing interactively, you check for expected results directly, by printing and inspecting your objects. Since tests are in their own objects, you need a way to programmatically look for problems. One way to accomplish this is to use the standard error handling mechanism (#error:) with testing logic to signal errors:

 
2 + 3 = 5 ifFalse: [self error: 'Wrong answer']

When you're testing, you'd like to distinguish between errors you are checking for, like getting six as the sum of two and three, and errors you didn't anticipate, like subscripts being out of bounds or messages not being understood.

There's not a lot you can do about unanticipated errors (if you did something about them, they wouldn't be unanticipated any more, would they?) When a catastrophic error occurs, the framework stops running the test case, records the error, and runs the next test case. Since each test case has its own fixture, the error in the previous case will not affect the next.

The testing framework makes checking for expected values simple by providing a method, #should:, that takes a Block as an argument. If the Block evaluates to true, everything is fine. Otherwise, the test case stops running, the failure is recorded, and the next test case runs.

So, you have to turn checks into a Block evaluating to a Boolean, and send the Block as the parameter to #should:.

In the example, after stimulating the fixture by adding an object to an empty Set, we want to check and make sure it's in there:

 
SetTestCasee>>#testAdd
    empty add: 5.
    self should: [empty includes: 5]

There is a variant on TestCase>>#should:. TestCase>>#shouldnt: causes the test case to fail if the Block argument evaluates to true. It is there so you don't have to use (...) not.

Once you have a test case this far, you can run it. Create an instance of your TestCase subclass, giving it the selector of the testing method. Send run to the resulting object:

 
(SetTestCase selector: #testAdd) run

If it runs to completion, the test worked. If you get a walkback, something went wrong.


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