googletesting: Testing on the Toilet: Prefer Testing Public APIs Over Implementation-Detail Classes

Testing on the Toilet: Prefer Testing Public APIs Over Implementation-Detail Classes

Wednesday, January 14, 2015

by Andrew Trenk

This article was adapted from a Google Testing on the Toilet (TotT) episode. You can download a printer-friendly version of this TotT episode and post it in your office. Does this class need to have tests? class UserInfoValidator {
public void validate(UserInfo info) {
if (info.getDateOfBirth().isInFuture()) { throw new ValidationException()); }
}
}what if its only user looks like this? public class UserInfoService {
private UserInfoValidator validator;
public void save(UserInfo info) {
validator.validate(info); // Throw an exception if the value is invalid.
writeToDatabase(info);
}
}it probably doesn’t need testsUserInfoServicethe class is an implementation detail, not a public APIA public API can be called by any number of usersYou want to make sure these are well-testedAn implementation-detail class exists only to support public APIsThese classes can sometimes be tested indirectlyTesting implementation-detail classes is still useful in many casesthey often don’t need to be tested in as much depth as a public API,UserInfoServiceUserInfonullnullUserInfoValidator.validateYou should also try to restrict the visibility of implementation-detail classes,Testing implementation-detail classes too often leads to a couple problemsCode is harder to maintain since you need to update tests more oftenIf you test a behavior only through an implementation-detail class, you may get false confidence in your codeYou also have to be more careful when refactoring

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Testing on the Toilet: Prefer Testing Public APIs Over Implementation-Detail Classes

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