docs: adding a testing infos file to guide everyone through tests

CONTRIBUTING.md

@@ -74,6 +74,9 @@ If you intend to compile for musl, you will need to use the flag
 is `cargo build --release --target=x86_64-unknown-linux-musl --features
 vendored-openssl,git`.
 
+If you want more information on the tests please read:
+[testing on eza](https://github.com/eza-community/eza/blob/main/TESTING.md)
+
 ## Creating a PR
 
 First, use the pull request template.

TESTING.md

@@ -0,0 +1,34 @@
+<!--
+SPDX-FileCopyrightText: 2024 Christina Sørensen, Martin Fillon
+SPDX-FileContributor: Christina Sørensen
+
+SPDX-License-Identifier: EUPL-1.2
+-->
+# Testing eza
+
+## Running tests
+
+In order to run the tests in eza you need:
+- [just](https://github.com/casey/just)
+- [nix](https://nixos.org)
+
+then either run:
+- `just itest`
+- `nix build -L trycmd-local`
+
+## Modifying tests
+
+In order to test your changes on eza, you will need to do one or multiple things in different cases.
+You will need the additional tool
+- [powertest](https://github.com/eza-community/powertest)
+
+You will also need to modify the `devtools/dir-generator.sh` file if you want to add some test cases
+
+### You added/modified an option
+
+Please run `just regen` to regenerate powertesting. Then look into `tests/gen` or `tests/cmd` for any tests not passing
+
+### You changed the output of eza
+
+Please run `nix build -L trydump` or `just idump`
+And lookout for any test no longer passing