feat: add batch write operations and unit test suite

.changeset/lazy-trees-lie.md

@@ -0,0 +1,5 @@
+---
+'fireworkers': minor
+---
+
+feat: add batch write operations and unit test suite

.firebaserc

@@ -0,0 +1,5 @@
+{
+  "projects": {
+    "default": "test-project"
+  }
+}

.github/workflows/ci.yml

@@ -2,11 +2,42 @@ name: CI
 
 on:
   pull_request:
+    branches:
+      - master
+      - main
 
 jobs:
   Lint:
     uses: finsweet/workflow-ci-lint/.github/workflows/lint.yml@main
 
-  # Comment this job out if your project doesn't have any tests.
-  # Tests:
-  #   uses: finsweet/workflow-ci-test/.github/workflows/test.yml@main
+  Typecheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 10
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: pnpm
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm check
+
+  Unit-Tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 10
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: pnpm
+      - uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: 21
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm test:unit

README.md

@@ -287,6 +287,85 @@ const todos = await Firestore.query(db, {
 });
 ```
 
+### batch(db)
+
+Creates a write batch, used for performing multiple writes as a single atomic unit.
+
+Implements the same functionality as Firestore's [writeBatch](https://firebase.google.com/docs/reference/js/firestore_.md#writebatch).
+
+#### db
+
+Type: `DB`
+
+The DB instance.
+
+#### batch.set(paths, fields, options?)
+
+Adds a set operation to the batch. If the document does not yet exist, it will be created. If you provide `merge: true`, the provided fields will be merged into the existing document.
+
+- `paths` — Type: `string[]` — The path segments to the document (e.g. `['todos', 'my-id']`).
+- `fields` — Type: `Record<string, any>` — The fields to write.
+- `options.merge` — Type: `boolean` (optional) — If `true`, merges into an existing document.
+
+#### batch.update(paths, fields)
+
+Adds an update operation to the batch. The document must already exist.
+
+- `paths` — Type: `string[]` — The path segments to the document.
+- `fields` — Type: `Record<string, any>` — The fields to update.
+
+#### batch.delete(paths)
+
+Adds a delete operation to the batch.
+
+- `paths` — Type: `string[]` — The path segments to the document.
+
+#### batch.commit()
+
+Commits all of the writes in this write batch as a single atomic unit. Returns a `CommitResponse` with `writeResults` and `commitTime`.
+
+A batch can only be committed once. After `commit()` is called, any further calls to `set`, `update`, `delete`, or `commit` will throw an error.
+
+```typescript
+const b = Firestore.batch(db);
+
+b.set(['todos', 'todo-1'], { title: 'First', completed: false });
+b.set(['todos', 'todo-2'], { title: 'Second', completed: true });
+b.update(['todos', 'existing-id'], { completed: true });
+b.delete(['todos', 'old-id']);
+
+const response = await b.commit();
+```
+
+---
+
+## Testing
+
+Unit tests run against the [Firebase Emulator Suite](https://firebase.google.com/docs/emulator-suite) using [Vitest](https://vitest.dev/).
+
+### Prerequisites
+
+- [Java](https://www.java.com/) (required by the Firebase Emulator)
+- [Firebase CLI](https://firebase.google.com/docs/cli) (installed as a dev dependency)
+
+### Running tests
+
+Run the full test suite (starts the emulator automatically):
+
+```bash
+pnpm test:unit
+```
+
+Run tests in watch mode (requires the emulator to be running separately):
+
+```bash
+# Terminal 1 — start the emulator
+pnpm emulators
+
+# Terminal 2 — run tests in watch mode
+pnpm test:unit:watch
+```
+
 ## TypeScript
 
 This library has first-class TypeScript support.

firebase.json

@@ -0,0 +1,15 @@
+{
+  "firestore": {
+    "rules": "firestore.rules"
+  },
+  "emulators": {
+    "firestore": {
+      "port": 8080,
+      "host": "127.0.0.1"
+    },
+    "ui": {
+      "enabled": true,
+      "port": 4000
+    }
+  }
+}

firestore.rules

@@ -0,0 +1,8 @@
+rules_version = '2';
+service cloud.firestore {
+  match /databases/{database}/documents {
+    match /{document=**} {
+      allow read, write: if true;
+    }
+  }
+}

package.json

@@ -43,10 +43,15 @@
     "format": "prettier --write ./src",
     "test": "pnpm playwright test",
     "test:headed": "pnpm playwright test --headed",
+    "test:unit": "firebase emulators:exec --only firestore --project test-project \"vitest run\"",
+    "test:unit:watch": "vitest",
+    "emulators": "firebase emulators:start --only firestore --project test-project",
     "release": "changeset publish",
     "update": "pnpm update -i -L -r"
   },
   "devDependencies": {
+    "firebase-tools": "15.15.0",
+    "vitest": "3.0.0",
     "@changesets/changelog-git": "^0.2.0",
     "@changesets/cli": "^2.27.12",
     "@eslint/js": "^9.19.0",