Try to replicate as closely as possible the CI setup

So that the hashes match

.github/workflows/test.yml

@@ -22,11 +22,9 @@ jobs:
         name: '${{ env.CACHIX_NAME }}'
         signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
         authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+    - run: cachix use nixos-nix-install-tests
     - run: nix-build -A checks.$(nix-instantiate --eval -E '(builtins.currentSystem)')
-    - run: |
-        cachix use nixos-nix-install-tests
-        CURRENT_NIX_BUILD=$(nix-build -A defaultPackage.$(nix-instantiate --eval -E '(builtins.currentSystem)'))/bin
-        PATH=$CURRENT_NIX_BUILD:$PATH GITHUB_TOKEN=${{ secrets.GITHUB_TOKEN }} bash scripts/test-against-master.sh
+    - run: bash scripts/test-against-master.sh
   check_cachix:
     name: Cachix secret present for installer tests
     runs-on: ubuntu-latest

scripts/test-against-master.sh

@@ -6,7 +6,7 @@ set -x;
 CurrentNixDir=$(pwd)
 CurrentRev=${GITHUB_SHA:-$(git rev-parse HEAD)}
 WorkDir=$(mktemp -d)
-trap 'rm -r "$WorkDir"' EXIT
+trap 'rm -rf "$WorkDir"' EXIT
 GITHUB_TOKEN_OPTION=()
 if [[ -n "${GITHUB_TOKEN:-}" ]]; then
     GITHUB_TOKEN_OPTION=("--option" "access-tokens" "github.com=$GITHUB_TOKEN")
@@ -14,20 +14,16 @@ fi
 
 pushd "$WorkDir"
 
-cat <<EOF > flake.nix
-{
-    inputs.currentNix.url = "git+file://$CurrentNixDir?rev=$CurrentRev";
-    inputs.nixMaster.url = "github:nixos/nix";
+git clone "https://github.com/nixos/nix"
 
-    outputs = { self, currentNix, nixMaster }: {
-        checks = builtins.mapAttrs (systemName: _:
-        { againstMaster = currentNix.lib.testAgainst.\${systemName} nixMaster.defaultPackage.\${systemName}; }
-        ) currentNix.defaultPackage;
-    };
-}
+cat <<EOF > default.nix
+let
+  currentNix = import $CurrentNixDir;
+  masterNix = import ./nix;
+in
+currentNix.lib.testAgainst.\${builtins.currentSystem} masterNix.defaultPackage.\${builtins.currentSystem}
 EOF
-nix flake check\
-    --experimental-features 'nix-command flakes' \
-    "${GITHUB_TOKEN_OPTION[@]}"
+
+nix-build "${GITHUB_TOKEN_OPTION[@]}"
 
 popd