add more info on how to run and write integration tests

docs/tutorials/integrationtests.md

@@ -10,3 +10,28 @@ You can find all integration tests under the [tests/integration](/tests/integrat
 ```console
 nix-build -A tests.integration.keycloak
 ```
+
+To run the "simple" integration test for keycloak, execute:
+
+```console
+nix-build -A tests.integration.keycloak.simple
+```
+
+## Write integration tests
+
+To create an integration test for disnix, you'll need:
+- a tarball,
+- a manifest build,
+- and a test definition with a test script written in Python.
+
+The [NixOS official
+documentation](https://nixos.org/manual/nixos/stable/index.html#sec-nixos-tests)
+has a complete reference on what python functions are available in the
+test script.
+
+To iterate on the test script, the easiest is by far to use the interactive mode by using the `.driverInteractive` attribute, like so:
+
+```console
+nix-build -A tests.integration.keycloak.simple.driverInteractive
+./result/bin/nixos-test-driver
+```