# tasty-mgolden
Text based [golden tests](https://ro-che.info/articles/2017-12-04-golden-tests)
for [tasty](https://github.com/feuerbach/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](https://github.com/feuerbach/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](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](example/example-a.txt)
```
foo
bar
```
Contents of [example/example-b.txt](example/example-b.txt)
```
foo
bar
```
Contents: `example/Test.hs`
```haskell
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:
```diff
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` ?