tasty-mgolden

Text based golden tests for tasty, with multi line (colored) diff expectation failure reporting.

Basically this package can turn any IO Text action into a golden test via providing a FilePath.

This package is the small brother of tasty-golden which also implements the same golden testing pattern.

tasty-mgolden is less generic and more opinionated than its bigger brother. But for that reason can also offer more ergonomic defaults for its core use case:

Golden testing for IO Text actions. Where:

• The text value is assuemd to contain multiple lines.
• The expectation failures can be rendered nicely in multi line diffs.
• The diff lines are colored via the tasty infrastructure
• The diff rendering is not done via the external diff command, but uses the Diff package.

Expectation diffs are rendered like developers are used to:

• Removed lines rendered in red.
• Added lines in green.

Usage

This is taken from the example directory in the repository.

To run these execute from repository root:

stack build
stack exec tasty-mgolden-example

Contents of example/example-a.txt

foo
bar

Contents of example/example-b.txt

foo
bar

Contents: example/Test.hs

import Test.Tasty
import Test.Tasty.MGolden

main :: IO ()
main = defaultMain $ testGroup "golden tests"
  [ goldenTest "example-a" "example/example-a.txt" $ pure "foo\nbar\n"
  , goldenTest "example-b" "example/example-b.txt" $ pure "foo\nbaz\n"
  ]

Output:

golden tests
  example-a: OK
  example-b: FAIL
 foo
-bar
+baz

1 out of 2 tests failed (0.00s)

Passing the --update flag to accept the changes:

golden tests
  example-a: OK
  example-b: OK
    UPDATE

All 2 tests passed (0.00s)

TODOs

PRs on these are welcome.

• Improve the multi line diff reporting to only show a minimal context around the changed hunks.
• Add line markers in unified diff format.
• Change to pathtype from filepath
• Future? Upstream this to tasty-golden ?