tests: Move NixOS tests to tests/nixos

This will allow contributors to find them more easily.

tests/nixos/nix-copy-closure.nix

@@ -0,0 +1,77 @@
+# Test ‘nix-copy-closure’.
+
+{ nixpkgs, system, overlay }:
+
+with import (nixpkgs + "/nixos/lib/testing-python.nix") {
+  inherit system;
+  extraConfigurations = [ { nixpkgs.overlays = [ overlay ]; } ];
+};
+
+makeTest (let pkgA = pkgs.cowsay; pkgB = pkgs.wget; pkgC = pkgs.hello; pkgD = pkgs.tmux; in {
+  name = "nix-copy-closure";
+
+  nodes =
+    { client =
+        { config, lib, pkgs, ... }:
+        { virtualisation.writableStore = true;
+          virtualisation.additionalPaths = [ pkgA pkgD.drvPath ];
+          nix.settings.substituters = lib.mkForce [ ];
+        };
+
+      server =
+        { config, pkgs, ... }:
+        { services.openssh.enable = true;
+          virtualisation.writableStore = true;
+          virtualisation.additionalPaths = [ pkgB pkgC ];
+        };
+    };
+
+  testScript = { nodes }: ''
+    # fmt: off
+    import subprocess
+
+    start_all()
+
+    # Create an SSH key on the client.
+    subprocess.run([
+      "${pkgs.openssh}/bin/ssh-keygen", "-t", "ed25519", "-f", "key", "-N", ""
+    ], capture_output=True, check=True)
+
+    client.succeed("mkdir -m 700 /root/.ssh")
+    client.copy_from_host("key", "/root/.ssh/id_ed25519")
+    client.succeed("chmod 600 /root/.ssh/id_ed25519")
+
+    # Install the SSH key on the server.
+    server.succeed("mkdir -m 700 /root/.ssh")
+    server.copy_from_host("key.pub", "/root/.ssh/authorized_keys")
+    server.wait_for_unit("sshd")
+    client.wait_for_unit("network.target")
+    client.succeed(f"ssh -o StrictHostKeyChecking=no {server.name} 'echo hello world'")
+
+    # Copy the closure of package A from the client to the server.
+    server.fail("nix-store --check-validity ${pkgA}")
+    client.succeed("nix-copy-closure --to server --gzip ${pkgA} >&2")
+    server.succeed("nix-store --check-validity ${pkgA}")
+
+    # Copy the closure of package B from the server to the client.
+    client.fail("nix-store --check-validity ${pkgB}")
+    client.succeed("nix-copy-closure --from server --gzip ${pkgB} >&2")
+    client.succeed("nix-store --check-validity ${pkgB}")
+
+    # Copy the closure of package C via the SSH substituter.
+    client.fail("nix-store -r ${pkgC}")
+
+    # Copy the derivation of package D's derivation from the client to the server.
+    server.fail("nix-store --check-validity ${pkgD.drvPath}")
+    client.succeed("nix-copy-closure --to server --gzip ${pkgD.drvPath} >&2")
+    server.succeed("nix-store --check-validity ${pkgD.drvPath}")
+
+    # FIXME
+    # client.succeed(
+    #   "nix-store --option use-ssh-substituter true"
+    #   " --option ssh-substituter-hosts root\@server"
+    #   " -r ${pkgC} >&2"
+    # )
+    # client.succeed("nix-store --check-validity ${pkgC}")
+  '';
+})