Bringing Jest-esque Snapshot testing to C#. See Project Site for more details
$ dotnet add package Snapper.NunitBringing Jest-esque Snapshot testing to C#
<!-- <p align="center"> Add logo here once I find/make one </p> <h2 align="center">Bringing Jest-esque Snapshot testing to C#</h2> -->Snapper is a NuGet library which makes snapshot testing very easy in C#. Snapshot testing can simplify testing and is super useful when paired with Golden Master testing or contract testing APIs. It is very heavily based on Jest Snapshot Testing framework.
See https://theramis.github.io/Snapper/ for the full documentation.
The best way to describe what Snapper does by going through an example. Imagine you have the following test where are retrieving a user from a service.
[Fact]
public void MyTest()
{
var myUser = _userService.GetUser(id);
Assert.Equal("MyUser", myUser.Username);
Assert.Equal("email@example.com", myUser.Email);
Assert.Equal("myhash", myUser.PasswordHash);
...
...
}
As you can imagine the assertion steps in the test can get very long and hard to read. Now lets see what the test would look like if Snapper is used.
<!-- ## Snapper V1 is deprecated After a lot of thought I've decided to deprecate Snapper V1. Snapper V1 was my first attempt at an OSS library and some of the decisions I made very early on made it very difficult to add new features. Snapper V2 is my second attempt at making the library easier to use and update. Snapper V1 consisted of the following NuGet packages all of which are deprecated: - Snapper.Core - Snapper.Json - Snapper.Json.Xunit - Snapper.Json.Nunit There is a migration guide available [here](https://theramis.github.io/Snapper/migration.html) The changes in V2 are documented in the [Changelog](https://theramis.github.io/Snapper/changelog.html) ## Todo - Add logo to Nuget - Write tests for testing json store. - Update V1 package descriptions to mention deprecated - Use appveyor logger on all test projects --> <!-- ALL-CONTRIBUTORS-LIST:START - Do not remove or modify this section --> <!-- prettier-ignore-start --> <!-- markdownlint-disable --> <table> <tr> <td align="center"><a href="https://github.com/fgather"><img src="https://avatars3.githubusercontent.com/u/614354?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Florian Gather</b></sub></a><br /><a href="https://github.com/theramis/Snapper/commits?author=fgather" title="Code">💻</a> <a href="#ideas-fgather" title="Ideas, Planning, & Feedback">🤔</a></td> <td align="center"><a href="https://www.linkedin.com/in/tomasbruckner/"><img src="https://avatars2.githubusercontent.com/u/7334618?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Tomas Bruckner</b></sub></a><br /><a href="https://github.com/theramis/Snapper/commits?author=tomasbruckner" title="Code">💻</a></td> <td align="center"><a href="https://visualon.de"><img src="https://avatars1.githubusercontent.com/u/1798109?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Michael Kriese</b></sub></a><br /><a href="https://github.com/theramis/Snapper/commits?author=ViceIce" title="Code">💻</a> <a href="#ideas-ViceIce" title="Ideas, Planning, & Feedback">🤔</a> <a href="https://github.com/theramis/Snapper/issues?q=author%3AViceIce" title="Bug reports">🐛</a></td> <td align="center"><a href="http://cognitoforms.com"><img src="https://avatars0.githubusercontent.com/u/4603206?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Taylor Kimmett</b></sub></a><br /><a href="https://github.com/theramis/Snapper/commits?author=tskimmett" title="Code">💻</a></td> <td align="center"><a href="https://github.com/PatrickLehnerXI"><img src="https://avatars1.githubusercontent.com/u/19566691?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Patrick Lehner</b></sub></a><br /><a href="https://github.com/theramis/Snapper/issues?q=author%3APatrickLehnerXI" title="Bug reports">🐛</a></td> <td align="center"><a href="https://github.com/plitwinski"><img src="https://avatars3.githubusercontent.com/u/25408297?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Piotr Litwinski</b></sub></a><br /><a href="https://github.com/theramis/Snapper/issues?q=author%3Aplitwinski" title="Bug reports">🐛</a></td> <td align="center"><a href="https://github.com/WarrenFerrell"><img src="https://avatars0.githubusercontent.com/u/8977001?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Warren Ferrell</b></sub></a><br /><a href="https://github.com/theramis/Snapper/commits?author=WarrenFerrell" title="Code">💻</a></td> </tr> <tr> <td align="center"><a href="https://github.com/lilasquared"><img src="https://avatars3.githubusercontent.com/u/3036779?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Aaron Roberts</b></sub></a><br /><a href="https://github.com/theramis/Snapper/commits?author=lilasquared" title="Code">💻</a> <a href="#ideas-lilasquared" title="Ideas, Planning, & Feedback">🤔</a></td> <td align="center"><a href="https://github.com/jaytulk"><img src="https://avatars.githubusercontent.com/u/34781842?v=4?s=100" width="100px;" alt=""/><br /><sub><b>jaytulk</b></sub></a><br /><a href="https://github.com/theramis/Snapper/commits?author=jaytulk" title="Code">💻</a></td> </tr> </table> <!-- markdownlint-restore --> <!-- prettier-ignore-end --> <!-- ALL-CONTRIBUTORS-LIST:END -->[Fact]
public void MyTest()
{
var myUser = _userService.GetUser(id);
myUser.ShouldMatchSnapshot();
}
The test above is now asserting the myUser object with a snapshot stored on disk. Snapper helps you create this snapshot at the beginnging (see Quick Start).
This is the basis of snapshot testing. The idea being a baseline is first generated (in this case a json file which is our snapshot) and then everytime the test runs the output is compared to the snapshot. If the snapshot and the output from the tests don't match the test fails!
As you can see using Snapper the test is now much smaller and easier to read but that's not all. Using Snapper brings with it a lot more benefits!
Benefits of using Snapper/snapshot testing vs traditional assertions
FirstName to the myUser object above. Using traditional assertions the test would still pass and it's easy to forget to update the test. Using Snapper the test would immediately fail since it's a change in the system and the developer should verify if the change was expected!Use cases where Snapper/snapshot testing really shines
The use cases above are just some of the examples I've found where Snapper is super useful. Feel free to try them in other situation you think would be useful.
Thanks goes to these wonderful people (emoji key):
This project follows the all-contributors specification. Contributions of any kind welcome!