[plt-scheme] ANN: SchemeUnit 3

From: Noel Welsh (noelwelsh at gmail.com)
Date: Mon Aug 4 15:12:35 EDT 2008

Hi all,

SchemeUnit 3 is out.  The emphasis for this release is making testing
really simple.  The docs are here:


A short essay (taken from the docs) explaining the new philosophy is
below.  Enjoy!


The Philosophy of SchemeUnit

SchemeUnit is designed to allow tests to evolve in step with the
evolution of the program under testing. SchemeUnit scales from the
unstructed checks suitable for simple programs to the complex
structure necessary for large projects.

Simple programs, such as those in How to Design Programs, are
generally purely functional with no setup required to obtain a context
in which the function may operate. Therefore the tests for these
programs are extremely simple: the test expressions are single checks,
usually for equality, and there are no dependencies between
expressions. For example, a HtDP student may be writing simple list
functions such as length, and the properties they are checking are of
the form:

  (equal? (length null) 0)

  (equal? (length '(a)) 1)

  (equal? (length '(a b)) 2)

SchemeUnit directly supports this style of testing. A check on its own
is a valid test. So the above examples may be written in SchemeUnit

  (check-equal? (length null) 0)

  (check-equal? (length '(a)) 1)

  (check-equal? (length '(a b)) 2)

Simple programs now get all the benefits of SchemeUnit with very
little overhead.

There are limitations to this style of testing that more complex
programs will expose. For example, there might be dependencies between
expressions, caused by state, so that it does not make sense to
evaluate some expressions if earlier ones have failed. This type of
program needs a way to group expressions so that a failure in one
group causes evaluation of that group to stop and immediately proceed
to the next group. In SchemeUnit all that is required is to wrap a
test-begin expression around a group of expressions:



    (check-equal? (foo! 1) 'expected-value-1)

    (check-equal? (foo! 2) 'expected-value-2))

Now if any expression within the test-begin expression fails no
further expressions in that group will be evaluated.

Notice that all the previous tests written in the simple style are
still valid. Introducing grouping is a local change only. This is a
key feature of SchemeUnit's support for the evolution of the program.

The programmer may wish to name a group of tests. This is done using
the test-case expression, a simple variant on test-begin:


    "The name"

    ... test expressions ...)

Most programs will stick with this style. However, programmers writing
very complex programs may wish to maintain separate groups of tests
for different parts of the program, or run their tests in different
ways to the normal SchemeUnit manner (for example, test results may be
logged for the purpose of improving software quality, or they may be
displayed on a website to indicate service quality). For these
programmers it is necessary to delay the execution of tests so they
can processed in the programmer's chosen manner. To do this, the
programmer simply wraps a test-suite around their tests:


    "Suite name"

    (check ...)

    (test-begin ...)

    (test-case ...))

The tests now change from expressions that are immediately evaluated
to objects that may be programmatically manipulated. Note again this
is a local change. Tests outside the suite continue to evaluate as

2.1 Historical Context

Most testing frameworks, including earlier versions of SchemeUnit,
support only the final form of testing. This is likely due to the
influence of the SUnit testing framework, which is the ancestor of
SchemeUnit and the most widely used frameworks in Java, .Net, Python,
and Ruby, and many other languages. That this is insufficient for all
users is apparent if one considers the proliferation of "simpler"
testing frameworks in Scheme such as SRFI-78, or the the practice of
beginner programmers. Unfortunately these simpler methods are
inadequate for testing larger systems. To the best of my knowledge
SchemeUnit is the only testing framework that makes a conscious effort
to support the testing style of all levels of programmer.

Posted on the users mailing list.