Check expected Nix versions using script

.editorconfig

@@ -0,0 +1,10 @@
+# https://editorconfig.org
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true

.github/verify-version.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env
+
+EXPECTED_VERSION="${1}"
+
+NIX_VERSION_OUTPUT=$(nix --version)
+NIX_VERSION=$(echo "${NIX_VERSION_OUTPUT}" | awk '{print $NF}')
+EXPECTED_OUTPUT="nix (Nix) ${EXPECTED_VERSION}"
+if [ "${NIX_VERSION_OUTPUT}" != "${EXPECTED_OUTPUT}" ]; then
+  echo "Nix version ${NIX_VERSION} didn't match expected version ${EXPECTED_VERSION}"
+  exit 1
+else
+  echo "Success! Nix version ${NIX_VERSION} installed as expected"
+fi

.github/workflows/ci.yml

@@ -222,37 +222,37 @@ jobs:
         uses: ./
         with:
           source-url: https://github.com/DeterminateSystems/nix-installer/releases/download/v0.18.0/nix-installer-x86_64-linux
-      - name: Ensure that Nix is installed via alternative source-url
+      - name: Ensure that the expected Nix version is installed via alternative source-url
-        run: nix --version
+        run: .github/verify-version.sh 2.18.0
 
       - name: Install with alternative source-pr
         uses: ./
         with:
           # https://github.com/DeterminateSystems/nix-installer/pull/938
           source-pr: "938"
-      - name: Ensure that Nix is installed via alternative source-pr
+      - name: Ensure that the expected Nix version is installed via alternative source-pr
-        run: nix --version
+        run: .github/verify-version.sh 2.21.2
 
       - name: Install with alternative source-revision
         uses: ./
         with:
           # https://github.com/DeterminateSystems/nix-installer/tree/ccf1d39a83099657ad324e7927676432435431e1
           source-revision: "ccf1d39a83099657ad324e7927676432435431e1"
-      - name: Ensure that Nix is installed via alternative source-revision
+      - name: Ensure that the expected Nix version is installed via alternative source-revision
-        run: nix --version
+        run: .github/verify-version.sh 2.21.2
 
       - name: Install with alternative source-branch
         uses: ./
         with:
           # https://github.com/DeterminateSystems/nix-installer/tree/lazy-trees
           source-revision: "lazy-trees"
-      - name: Ensure that Nix is installed via alternative source-branch
+      - name: Ensure that the expected Nix version is installed via alternative source-branch
-        run: nix --version
+        run: .github/verify-version.sh 2.21.2
 
       - name: Install with alternative source-tag
         uses: ./
         with:
           # https://github.com/DeterminateSystems/nix-installer/tree/v0.14.0
           source-tag: "v0.14.0"
-      - name: Ensure that Nix is installed via alternative source-tag
+      - name: Ensure that the expected Nix version is installed via alternative source-tag
-        run: nix --version
+        run: .github/verify-version.sh 2.18.0