5 RackUnit Internals and Extension API

▼ |  | Rack Unit: Unit Testing

1 | Quick Start Guide for Rack Unit
2 | The Philosophy of Rack Unit
3 | Rack Unit API
4 | Testing Utilities
5 | Rack Unit Internals and Extension API
6 | Release Notes
7 | Acknowlegements
| Index

► | 5 | Rack Unit Internals and Extension API

5.1 | Customizing Check Evaluation
5.2 | Customizing Test Evaluation
5.3 | Programmatically Running Tests and Inspecting Results

On this page:

5.1 Customizing Check Evaluation
current-check-handler
current-check-around
5.2 Customizing Test Evaluation
current-test-name
current-test-case-around
test-suite-test-case-around
test-suite-check-around
5.3 Programmatically Running Tests and Inspecting Results
5.3.1 Result Types
exn: test
exn: test: check
test-result
test-failure
test-error
test-success
5.3.2 Functions to Run Tests
run-test-case
run-test
fold-test-results
foldts-test-suite

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## 5 RackUnit Internals and Extension API🔗ℹ

This section describes RackUnit’s facilities for customizing the behavior of checks and tests and for creating new kinds of test runners.

### 5.1 Customizing Check Evaluation🔗ℹ

The semantics of checks are determined by the parameters current-check-around and current-check-handler. Other testing form such as test-begin and test-suite change the value of these parameters.

> parameter (current-check-handler) → (-> any/c any)
> (current-check-handler handler) → void?
> handler : (-> any/c any)

Parameter containing the function that handles exceptions raised by check failures. The default value is a procedure that will display the exception data in a user-friendly format.

> parameter (current-check-around) → (-> (-> any) any)
> (current-check-around check) → void?
> check : (-> (-> any) any)

Parameter containing the function that handles the execution of checks. The default value wraps the evaluation of thunk in a with-handlers call that calls current-check-handler if an exception is raised and then (when an exception is not raised) discards the result, returning (void).

### 5.2 Customizing Test Evaluation🔗ℹ

Just like with checks, there are several parameters that control the semantics of compound testing forms.

> parameter (current-test-name) → (or/c string? false/c)
> (current-test-name name) → void?
> name : (or/c string? false/c)

This parameter stores the name of the current test case. A value of #f indicates a test case with no name, such as one constructed by test-begin.

> parameter (current-test-case-around) → (-> (-> any) any)
> (current-test-case-around handler) → void?
> handler : (-> (-> any) any)

This parameter handles evaluation of test cases. The value of the parameter is a function that is passed a thunk (a function of no arguments). The function, when applied, evaluates the expressions within a test case. The default value of the current-test-case-around parameters evaluates the thunk in a context that catches exceptions and prints an appropriate message indicating test case failure.

> procedure (test-suite-test-case-around thunk) → any
> thunk : (-> any)

The current-test-case-around parameter is parameterized to this value within the scope of a test-suite. This function creates a test case structure instead of immediately evaluating the thunk.

> procedure (test-suite-check-around thunk) → any/c
> thunk : (-> any/c)

The current-check-around parameter is parameterized to this value within the scope of a test-suite. This function creates a test case structure instead of immediately evaluating a check.

### 5.3 Programmatically Running Tests and Inspecting Results🔗ℹ

RackUnit provides an API for running tests, from which custom UIs can be created.

#### 5.3.1 Result Types🔗ℹ

> > struct
> > (struct |  | exn:test exn:fail ()
> #:extra-constructor-name make-exn:test)

The base structure for RackUnit exceptions. You should never catch instances of this type, only the subtypes documented below.

> > struct
> > (struct |  | exn:test:check exn:test (stack)
> #:extra-constructor-name make-exn:test:check)
> stack : (listof check-info)

A exn:test:check is raised when an check fails, and contains the contents of the check-info stack at the time of failure.

> > struct
> > (struct |  | test-result (test-case-name)
> #:extra-constructor-name make-test-result)
> test-case-name : (or/c string #f)

A test-result is the result of running the test with the given name (with #f indicating no name is available).

> > struct
> > (struct |  | test-failure test-result (result)
> #:extra-constructor-name make-test-failure)
> result : any

Subtype of test-result representing a test failure.

> > struct
> > (struct |  | test-error test-result (result)
> #:extra-constructor-name make-test-error)
> result : exn

Subtype of test-result representing a test error.

> > struct
> > (struct |  | test-success test-result (result)
> #:extra-constructor-name make-test-success)
> result : any

Subtype of test-result representing a test success.

#### 5.3.2 Functions to Run Tests🔗ℹ

> procedure (run-test-case name action) → test-result
> name : (or/c string #f)
> action : (-> any)

Runs the given test case, returning a result representing success, failure, or error.

> procedure (run-test test)
> → (flat-murec-contract ([R (listof (or/c test-result? R))]) R)
> test : (or/c test-case? test-suite?)

Runs the given test (test case or test suite) returning a tree (list of lists) of results

Example:

> (run-test
> (test-suite
> "Dummy"
> (test-case "Dummy" (check-equal? 1 2))))

> > procedure
> > (fold-test-results |  | result-fn |  |  |  |
> > |  | seed |  |  |  |
> > |  | test |  |  |  |
> > |  | #:run run |  |  |  |
> > |  | #:fdown fdown |  |  |  |
> > |  | #:fup fup) |  | → |  | 'a
> result-fn : ('b 'c ... 'a . -> . 'a)
> seed : 'a
> test : (or/c test-case? test-suite?)
> run : (string (() -> any) . -> . 'b 'c ...)
> fdown : (string 'a . -> . 'a)
> fup : (string 'a . -> . 'a)

Fold result-fn pre-order left-to-right depth-first over the results of run. By default run is run-test-case and fdown and fup just return the seed, so result-fn is folded over the test results.

This function is useful for writing custom folds (and hence UIs) over test results without you having to take care of all the expected setup and teardown. For example, fold-test-results will run test suite before and after actions for you. However it is still flexible enough, via its keyword arguments, to do almost anything that foldts-test-suite can. Hence it should be used in preference to foldts-test-suite.

The result-fn argument is a function from the results of run (defaults to a test-result) and the seed to a new seed.

The seed argument is any value.

The test argument is a test case or test suite.

The run argument is a function from a test case name (string) and action (thunk) to any values. The values produced by run are fed into the result-fn.

The fdown argument is a function from a test suite name (string) and the seed, to a new seed.

The fup argument is a function from a test suite name (string) and the seed, to a new seed.

Examples:

The following code counts the number of successes:

> (define (count-successes test)
> (fold-test-results
> (lambda (result seed)
> (if (test-success? result)
> (add1 seed)
> seed))
> 0
> test))

The following code returns the symbol 'burp instead of running test cases. Note how the result-fn receives the value of run.

> (define (burp test)
> (fold-test-results
> (lambda (result seed) (cons result seed))
> null
> test
> #:run (lambda (name action) 'burp)))

> procedure (foldts-test-suite fdown fup fhere seed test) → 'a
> fdown : (test-suite string thunk thunk 'a -> 'a)
> fup : (test-suite string thunk thunk 'a 'a -> 'a)
> fhere : (test-case string thunk 'a -> 'a)
> seed : 'a
> test : (or/c test-case? test-suite?)

The foldts-test-suite function is a nifty tree fold (created by Oleg Kiselyov) that folds over a test in a useful way (fold-test-results isn’t that useful as you can’t specify actions around test cases).

The fdown argument is a function of test suite, test suite name, before action, after action, and the seed. It is run when a test suite is encountered on the way down the tree (pre-order).

The fup argument is a function of test suite, test suite name, before action, after action, the seed at the current level, and the seed returned by the children. It is run on the way up the tree (post-order).

The fhere argument is a function of the test case, test case name, the test case action, and the seed. (Note that this might change in the near future to just the test case. This change would be to allow fhere to discriminate subtypes of test-case, which in turn would allow test cases that are, for example, ignored).

Example:

Here’s the implementation of fold-test-results in terms of foldts-test-suite:

> (define (fold-test-results suite-fn case-fn seed test)
> (foldts-test-suite
> (lambda (suite name before after seed)
> (before)
> (suite-fn name seed))
> (lambda (suite name before after seed kid-seed)
> (after)
> kid-seed)
> (lambda (case name action seed)
> (case-fn
> (run-test-case name action)
> seed))
> seed
> test))

If you’re used to folds you’ll probably be a bit surprised that the functions you pass to foldts-test-suite receive both the structure they operate on, and the contents of that structure. This is indeed unusual. It is done to allow subtypes of test-case and test-suite to be run in customised ways. For example, you might define subtypes of test case that are ignored (not run), or have their execution time recorded, and so on. To do so the functions that run the test cases need to know what type the test case has, and hence is is necessary to provide this information.

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