Basic deployment test: Introduce a “flake under test”, overriding /flake.nix

deployment/check/basic/flake-part.nix

@@ -11,9 +11,4 @@
         inherit inputs sources;
       };
     };
-
-  nixops4Deployments.check-deployment-basic = {
-    imports = [ ./deployment.nix ];
-    _module.args = { inherit inputs sources; };
-  };
 }

deployment/check/basic/flake-under-test.nix

@@ -0,0 +1,22 @@
+{
+  inputs = {
+    nixops4.follows = "nixops4-nixos/nixops4";
+    nixops4-nixos.url = "github:nixops4/nixops4-nixos";
+  };
+
+  outputs =
+    inputs:
+    import ./mkFlake.nix inputs (
+      { inputs, sources, ... }:
+      {
+        imports = [
+          inputs.nixops4.modules.flake.default
+        ];
+
+        nixops4Deployments.check-deployment-basic = {
+          imports = [ ./deployment/check/basic/deployment.nix ];
+          _module.args = { inherit inputs sources; };
+        };
+      }
+    );
+}

deployment/check/common/nixosTest.nix

@@ -134,7 +134,8 @@ in
 
       ## NOTE: This is super slow. It could probably be optimised in Nix, for
       ## instance by allowing to grab things directly from the host's store.
-      with subtest("Override the lock"):
+      with subtest("Override the flake and its lock"):
+        deployer.succeed("cp ${config.pathFromRoot}/flake-under-test.nix flake.nix")
         deployer.succeed("""
           nix flake lock --extra-experimental-features 'flakes nix-command' \
             --offline -v \