Add unimported to workflow (#2441)

* Remove unused file: lib/sinon/blob.js

The last reference to this file was removed in 6b1841f, making it safe to remove

* Move getConfig into test/

This has only been in use by tests since e37e1a6, so doesn't belong in the src/ folder anymore

* Remove unused lib/sinon/util/core/restore.js

Searching the git history, we find that the last reference to this file
was removed with e37e1a6.

```
git log -p --full-history --all -G'require.*restore"' li
```

Therefore, it is safe to remove the file.

* Add check for unimported files

This allows us to find files that are no longer in use in the project
and can be safely removed.

See https://github.com/smeijer/unimported

* fixup! Remove unused lib/sinon/util/core/restore.js

.github/workflows/main.yml

@@ -6,7 +6,7 @@ on:
       - master
   pull_request:
     branches:
-      - '**'
+      - "**"
 
 jobs:
   prettier:
@@ -56,6 +56,29 @@ jobs:
         run: |
           npm run lint
 
+  unused:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2
+        with:
+          node-version: "lts/*"
+      - name: Cache modules
+        uses: actions/cache@v2
+        with:
+          path: ~/.npm
+          key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-node-
+      - name: Install dependencies
+        run: |
+          npm ci
+        env:
+          PUPPETEER_SKIP_CHROMIUM_DOWNLOAD: 1
+      - name: Find unused files
+        run: |
+          npm run unimported
+
   browser-test:
     runs-on: ubuntu-latest
     steps:

.unimportedrc.json

@@ -0,0 +1,8 @@
+{
+  "entry": ["lib/sinon.js", "lib/sinon-esm.js"],
+  "extensions": [".js"],
+  "ignorePatterns": ["**/node_modules/**"],
+  "ignoreUnresolved": [],
+  "ignoreUnimported": ["docs/**", "pkg/**", "test/**"],
+  "ignoreUnused": []
+}