Safe Haskell	None
Language	Haskell2010

Test.Tasty.HUnit

Contents

Constructing test cases
Constructing assertions
Data types
Accurate location for domain-specific assertion functions
Deprecated functions and types

Description

Unit testing support for tasty, inspired by the HUnit package.

Here's an example (a single tasty test case consisting of three assertions):

import Test.Tasty
import Test.Tasty.HUnit

main = defaultMain $
  testCase "Example test case" $ do
    -- assertion no. 1 (passes)
    2 + 2 @?= 4
    -- assertion no. 2 (fails)
    assertBool "the list is not empty" $ null [1]
    -- assertion no. 3 (would have failed, but won't be executed because
    -- the previous assertion has already failed)
    "foo" @?= "bar"

Synopsis

testCase :: TestName -> Assertion -> TestTree
testCaseInfo :: TestName -> IO String -> TestTree
testCaseSteps :: TestName -> ((String -> IO ()) -> Assertion) -> TestTree
assertFailure :: HasCallStack => String -> IO a
assertBool :: HasCallStack => String -> Bool -> Assertion
assertEqual :: (Eq a, Show a, HasCallStack) => String -> a -> a -> Assertion
(@=?) :: (Eq a, Show a, HasCallStack) => a -> a -> Assertion
(@?=) :: (Eq a, Show a, HasCallStack) => a -> a -> Assertion
(@?) :: (AssertionPredicable t, HasCallStack) => t -> String -> Assertion
class AssertionPredicable t where
- assertionPredicate :: t -> IO Bool
type Assertion = IO ()
data HUnitFailure = HUnitFailure (Maybe SrcLoc) String
type HasCallStack = ?callStack :: CallStack
assertString :: HasCallStack => String -> Assertion
class Assertable t where
- assert :: t -> Assertion
type AssertionPredicate = IO Bool

Constructing test cases

testCase :: TestName -> Assertion -> TestTree #

Turn an Assertion into a tasty test case

testCaseInfo :: TestName -> IO String -> TestTree #

Like testCase, except in case the test succeeds, the returned string will be shown as the description. If the empty string is returned, it will be ignored.

testCaseSteps :: TestName -> ((String -> IO ()) -> Assertion) -> TestTree #

Create a multi-step unit test.

Example:

main = defaultMain $ testCaseSteps "Multi-step test" $ \step -> do
  step "Preparing..."
  -- do something

  step "Running part 1"
  -- do something

  step "Running part 2"
  -- do something
  assertFailure "BAM!"

  step "Running part 3"
  -- do something

The step calls are mere annotations. They let you see which steps were performed successfully, and which step failed.

You can think of step as putStrLn, except putStrLn would mess up the output with the console reporter and get lost with the others.

For the example above, the output will be

Multi-step test: FAIL
  Preparing...
  Running part 1
  Running part 2
    BAM!

1 out of 1 tests failed (0.00s)

Note that:

Tasty still treats this as a single test, even though it consists of multiple steps.
The execution stops after the first failure. When we are looking at a failed test, we know that all displayed steps but the last one were successful, and the last one failed. The steps after the failed one are not displayed, since they didn't run.

Constructing assertions

assertFailure #

Arguments

:: HasCallStack
=> String	A message that is displayed with the assertion failure
-> IO a

Unconditionally signals that a failure has occured. All other assertions can be expressed with the form:

   if conditionIsMet
       then return ()
       else assertFailure msg

assertBool #

Arguments

:: HasCallStack
=> String	The message that is displayed if the assertion fails
-> Bool	The condition
-> Assertion

Asserts that the specified condition holds.

assertEqual #

Arguments

:: (Eq a, Show a, HasCallStack)
=> String	The message prefix
-> a	The expected value
-> a	The actual value
-> Assertion

Asserts that the specified actual value is equal to the expected value. The output message will contain the prefix, the expected value, and the actual value.

If the prefix is the empty string (i.e., ""), then the prefix is omitted and only the expected and actual values are output.

(@=?) infix 1 #

Arguments

:: (Eq a, Show a, HasCallStack)
=> a	The expected value
-> a	The actual value
-> Assertion

Asserts that the specified actual value is equal to the expected value (with the expected value on the left-hand side).

(@?=) infix 1 #

Arguments

:: (Eq a, Show a, HasCallStack)
=> a	The actual value
-> a	The expected value
-> Assertion

Asserts that the specified actual value is equal to the expected value (with the actual value on the left-hand side).

(@?) infix 1 #

Arguments

:: (AssertionPredicable t, HasCallStack)
=> t	A value of which the asserted condition is predicated
-> String	A message that is displayed if the assertion fails
-> Assertion

An infix and flipped version of assertBool. E.g. instead of

assertBool "Non-empty list" (null [1])

you can write

null [1] @? "Non-empty list"

@? is also overloaded to accept IO Bool predicates, so instead of

do
  e <- doesFileExist "test"
  e @? "File does not exist"

you can write

doesFileExist "test" @? "File does not exist"

class AssertionPredicable t where #

An ad-hoc class used to overload the @? operator.

The only intended instances of this class are Bool and IO Bool.

You shouldn't need to interact with this class directly.

Methods

assertionPredicate :: t -> IO Bool #

Instances

AssertionPredicable Bool #
Instance details Defined in Test.Tasty.HUnit.Orig Methods assertionPredicate :: Bool -> IO Bool #
AssertionPredicable t => AssertionPredicable (IO t) #
Instance details Defined in Test.Tasty.HUnit.Orig Methods assertionPredicate :: IO t -> IO Bool #

Data types

type Assertion = IO () #

An assertion is simply an IO action. Assertion failure is indicated by throwing an exception, typically HUnitFailure.

Instead of throwing the exception directly, you should use functions like assertFailure and assertBool.

Test cases are composed of a sequence of one or more assertions.

data HUnitFailure #

Exception thrown by assertFailure etc.

Constructors

HUnitFailure (Maybe SrcLoc) String

Instances

Eq HUnitFailure #
Instance details Defined in Test.Tasty.HUnit.Orig Methods (==) :: HUnitFailure -> HUnitFailure -> Bool # (/=) :: HUnitFailure -> HUnitFailure -> Bool #
Show HUnitFailure #
Instance details Defined in Test.Tasty.HUnit.Orig Methods showsPrec :: Int -> HUnitFailure -> ShowS # show :: HUnitFailure -> String # showList :: [HUnitFailure] -> ShowS #
Exception HUnitFailure #
Instance details Defined in Test.Tasty.HUnit.Orig Methods toException :: HUnitFailure -> SomeException # fromException :: SomeException -> Maybe HUnitFailure # displayException :: HUnitFailure -> String #

Accurate location for domain-specific assertion functions

It is common to define domain-specific assertion functions based on the standard ones, e.g.

assertNonEmpty = assertBool "List is empty" . not . null

The problem is that if a test fails, tasty-hunit will point to the definition site of assertNonEmpty as the source of failure, not its use site.

To correct this, add a HasCallStack constraint (re-exported from this module) to your function:

assertNonEmpty :: HasCallStack => [a] -> Assertion
assertNonEmpty = assertBool "List is empty" . not . null

type HasCallStack = ?callStack :: CallStack #

Request a CallStack.

NOTE: The implicit parameter ?callStack :: CallStack is an implementation detail and should not be considered part of the CallStack API, we may decide to change the implementation in the future.

Since: base-4.9.0.0

Deprecated functions and types

These definitions come from HUnit, but I don't see why one would need them. If you have a valid use case for them, please contact me or file an issue for tasty. Otherwise, they will eventually be removed.

assertString #

Arguments

:: HasCallStack
=> String	The message that is displayed with the assertion failure
-> Assertion

Deprecated: Why not use assertBool instead?

Signals an assertion failure if a non-empty message (i.e., a message other than "") is passed.

class Assertable t where #

Deprecated: This class or type seems dubious. If you have a good use case for it, please create an issue for tasty. Otherwise, it may be removed in a future version.

Allows the extension of the assertion mechanism.

Since an Assertion can be a sequence of Assertions and IO actions, there is a fair amount of flexibility of what can be achieved. As a rule, the resulting Assertion should be the body of a TestCase or part of a TestCase; it should not be used to assert multiple, independent conditions.

If more complex arrangements of assertions are needed, Tests and Testable should be used.

Methods

assert :: t -> Assertion #

Instances

Assertable Bool #
Instance details Defined in Test.Tasty.HUnit.Orig Methods assert :: Bool -> Assertion #
Assertable () #
Instance details Defined in Test.Tasty.HUnit.Orig Methods assert :: () -> Assertion #
Assertable String #
Instance details Defined in Test.Tasty.HUnit.Orig Methods assert :: String -> Assertion #
Assertable t => Assertable (IO t) #
Instance details Defined in Test.Tasty.HUnit.Orig Methods assert :: IO t -> Assertion #

type AssertionPredicate = IO Bool #

Deprecated: This class or type seems dubious. If you have a good use case for it, please create an issue for tasty. Otherwise, it may be removed in a future version.

The result of an assertion that hasn't been evaluated yet.

Most test cases follow the following steps:

Do some processing or an action.
Assert certain conditions.

However, this flow is not always suitable. AssertionPredicate allows for additional steps to be inserted without the initial action to be affected by side effects. Additionally, clean-up can be done before the test case has a chance to end. A potential work flow is:

Write data to a file.
Read data from a file, evaluate conditions.
Clean up the file.
Assert that the side effects of the read operation meet certain conditions.
Assert that the conditions evaluated in step 2 are met.