Note: This post refers to testing and checking in the Rapid Software Testing namespace. This post has received a few minor edits since it was first posted.

For those disinclined to read Testing and Checking Refined, here are the definitions of testing and checking as defined by me and James Bach within the Rapid Software Testing namespace.

Testing is the process of evaluating a product by learning about it through exploration and experimentation, which includes to some degree: questioning, study, modeling, observation, inference, etc.

(A test is an instance of testing.)

Checking is the process of making evaluations by applying algorithmic decision rules to specific observations of a product.

(A check is an instance of checking.)

You are not checking. Well, you are probably not checking; you are certainly not only checking. You might be trying to do checking. Yet even if you are being asked to do checking, or if you think you’re doing checking, you will probably fail to do checking, because you are a human.

You can do things that could be encoded as checks, but you will do many other things too, at the same time. You won’t be able to restrict yourself to doing only checking.

Checking is a part of testing that can be performed entirely algorithmically. Remember that: checking is a part of testing that can be performed entirely algorithmically.

The exact parallel to that in programming is compiling: compiling is a part of programming that can be performed entirely algorithmically. No one talks of “automated compiling”, certainly not anymore. It is routine to think of compiling as an activity performed by a machine.

We still speak of “automated checking” because we have only recently introduced “checking” as a term of art. We say “automated checking” to emphasize that checking by definition can be, and in practice probably should be, automated.

If you are trying to do only checking, you will screw it up, because you are not a robot. Your humanity—your faculties that allow you to make unprogrammed observations and evaluations; your tendency to vary your behaviour; your capacity to identify unanticipated risks—will prevent you from living to an algorithm.

As a human tester—not a robot—you’re essentially incapable of sticking strictly to what you’ve been programmed to do. You will inevitably think or notice or conjecture or imagine or learn or evaluate or experiment or explore. At that point, you will have jumped out of checking and into the wider activities of testing.

(What you do with the outcome of your testing is up to you, but we’d say that if your testing produces information that might matter to a client, you should probably follow up on it and report it.)

Your unreliability and your variability is, for testing, a good thing. Human variability is a big reason why you’ll find bugs even when you’re following a script that the scriptwriter—presumably—completed successfully. (In our experience, if there’s a test script, someone has probably tried to perform it and has run through it successfully at least once.)

So, unless you’ve given up your humanity, it is very unlikely that you are only checking. What’s more likely is that you are testing. There are specific observations that you may be performing, and there are specific decision rules that you may be applying. Those are checks, and you might be performing them as tactics in your testing.

Many of your checks will happen below the level of your awareness. But just as it would be odd to describe someone’s activities at the dinner table as “biting” when they were eating, it would be odd to say that you were “checking” when you were testing.

Perhaps another one of your tactics, while testing, is programming a computer—or using a computer that someone else has programmed—to perform checking. In Rapid Software Testing, people who develop checks are generally called toolsmiths, or technical testers—people who are not intimidated by technology or code.

Remember: checking is a part of testing that can be performed entirely algorithmically. Therefore, if you’re a human, neither instructing the machine to start checking nor developing checks is “doing checking”.

Testers who develop checks are not “doing checking”. The checks themselves are algorithmic, and they are performed algorithmically by machinery, but the testers are not following algorithms as they develop checks, or deciding that a check should be performed, or evaluating the outcome of the checking. Similarly, programmers who develop classes and functions are not “doing compiling”. Those programmers are not following algorithms to produce code.

Toolsmiths who develop tools and frameworks for checking, and who program checks, are not “doing checking” either. Developers who produce tools and compilers for compiling are not “doing compiling”. Testers who produce checking tools should be seen as skilled specialists, just as developers who produce compilers are seen as skilled specialists. In order to develop excellent checks and excellent checking tools, a tester needs two distinct kinds of expertise: testing expertise, and programming and development expertise.

Testers apply checking as tactic of testing. Checking is embedded within a host of testing activities: modeling the test space; identifying risks; framing questions that can be asked about the product; encoding those questions in terms of algorithmic actions, observations, outcomes, and reports; choosing when the checking should be done; interpreting the outcome of checks, whether green or red.

Notice that checking does not find bugs. Testers—or developers temporarily in a testing role or a testing mindset—who apply checking find bugs, and the checks (and the checking) play a role in finding bugs.

In all of our talk about testing and checking, we are not attempting to diminish the role of people who create and use testing tools, including checks and checking. Nothing could be farther from the truth. Tools are vital to testing. Tools support testing.

We are, however, asking that testing not be reduced to checking. Checking is not testing, just as compiling is not software development. Checking may be a very important tactic in our testing, and as such, it is crucial to consider how it can be done expertly to assist our testing. It is important to consider the extents and limits of what checking can do for us. Testing a whole product while being fixated on checking is like like developing a whole product while being fixated on compiling.

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