Add custom planner test

.github/workflows/ci.yml

@@ -75,6 +75,81 @@ jobs:
           grep -E "^trusted-users = .*$USER" /etc/nix/nix.conf
           grep -E "^use-sqlite-wal = true" /etc/nix/nix.conf
 
+  run-steam-deck:
+    name: Run Steam Deck (Mock))
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v3
+      - name: Make the CI look like a steam deck
+        run: |
+          mkdir -p ~/bin
+          echo -e "#! /bin/sh\nexit 0" | sudo tee -a /bin/steamos-readonly
+          sudo chmod +x /bin/steamos-readonly
+          sudo useradd -m deck
+      - name: Install Nix
+        uses: ./
+        with:
+          logger: pretty
+          log-directives: nix_installer=trace
+          backtrace: full
+          nix-installer-branch: main
+      - name: echo $PATH
+        run: echo $PATH
+      - name: Test `nix` with `$GITHUB_PATH`
+        if: success() || failure()
+        run: |
+          nix run nixpkgs#hello
+          nix profile install nixpkgs#hello
+          hello
+          nix store gc
+          nix run nixpkgs#hello
+      - name: Test bash
+        run: nix-instantiate -E 'builtins.currentTime' --eval
+        if: success() || failure()
+        shell: bash --login {0}
+      - name: Test sh
+        run: nix-instantiate -E 'builtins.currentTime' --eval
+        if: success() || failure()
+        shell: sh -l {0}
+      - name: Install Nix again (noop)
+        uses: ./
+        with:
+          logger: pretty
+          log-directives: nix_installer=trace
+          backtrace: full
+          nix-installer-branch: main
+      - name: Test `nix` with `$GITHUB_PATH`
+        if: success() || failure()
+        run: |
+          nix run nixpkgs#hello
+          nix profile install nixpkgs#hello
+          hello
+          nix store gc
+          nix run nixpkgs#hello
+      - name: Reinstall Nix
+        uses: ./
+        with:
+          logger: pretty
+          log-directives: nix_installer=trace
+          backtrace: full
+          reinstall: true
+          extra-conf: |
+            use-sqlite-wal = true
+          nix-installer-branch: main
+      - name: Test `nix` with `$GITHUB_PATH`
+        if: success() || failure()
+        run: |
+          nix run nixpkgs#hello
+          nix profile install nixpkgs#hello
+          hello
+          nix store gc
+          nix run nixpkgs#hello
+      - name: Verify the generated nix.conf
+        run: |
+          cat -n /etc/nix/nix.conf
+          grep -E "^trusted-users = .*$USER" /etc/nix/nix.conf
+          grep -E "^use-sqlite-wal = true" /etc/nix/nix.conf
+
   run-x86_64-darwin:
     name: Run x86_64 Darwin
     runs-on: macos-12