ci: add end-to-end test for all templates

.github/actions/end-to-end/action.yml

@@ -0,0 +1,28 @@
+name: End-to-end Test
+description: End-to-end test for templates
+inputs:
+  name:
+    description: The directory name of the template
+    required: true
+
+runs:
+  using: composite
+  steps:
+    - uses: cachix/install-nix-action@v31
+    - name: Run end-to-end tests in nix environment
+      shell: nix shell nixpkgs#direnv --quiet --command bash {0}
+      run: |
+        # Create a directory for testing.
+        temp_dir="end-to-end"
+        mkdir "$temp_dir" && cd "$temp_dir"
+        # Download the template files.
+        echo "# ----- nix flake init ----- #"
+        nix flake init --template github:whisperpine/dev-templates#${{ inputs.name }}
+        # Track the "flake.nix" file by git.
+        git -C "$GITHUB_WORKSPACE" add "$temp_dir/flake.nix"
+        # Test the "nix develop" command.
+        echo "# ----- nix develop ----- #"
+        nix develop --quiet
+        # Test the "direnv allow" command.
+        echo "# ----- direnv allow ----- #"
+        direnv allow . && eval "$(direnv hook bash)"

.github/workflows/end-to-end.yml

@@ -0,0 +1,52 @@
+name: End to End
+
+on:
+  pull_request:
+  push:
+    branches: ["main"]
+
+jobs:
+  template-empty:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - name: Run end-to-end tests in nix environment
+        uses: ./.github/actions/end-to-end
+        with:
+          name: empty
+
+  template-golang:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - name: Run end-to-end tests in nix environment
+        uses: ./.github/actions/end-to-end
+        with:
+          name: golang
+
+  template-python:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - name: Run end-to-end tests in nix environment
+        uses: ./.github/actions/end-to-end
+        with:
+          name: python
+
+  template-rust:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - name: Run end-to-end tests in nix environment
+        uses: ./.github/actions/end-to-end
+        with:
+          name: rust
+
+  template-web:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - name: Run end-to-end tests in nix environment
+        uses: ./.github/actions/end-to-end
+        with:
+          name: web