Auto ID for document()

lib/src/mock_collection_reference.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'dart:math';
 
 import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:cloud_firestore_platform_interface/cloud_firestore_platform_interface.dart';
@@ -31,8 +32,21 @@ class MockCollectionReference extends MockQuery implements CollectionReference {
             .map((entry) => MockDocumentSnapshot(entry.key, entry.value))
             .toList());
 
+  static final Random _random = Random();
+  static final String _autoIdCharacters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
+  static String _generateAutoId() {
+    final maxIndex = _autoIdCharacters.length - 1;
+    final autoId = List<int>.generate(20, (_) => _random.nextInt(maxIndex))
+      .map((i) => _autoIdCharacters[i]).join();
+    return autoId;
+  }
+
   @override
   DocumentReference document([String path]) {
+    if (path == null) {
+      path = _generateAutoId();
+    }
+
     return MockDocumentReference(path, getSubpath(root, path), root,
         getSubpath(snapshotStreamControllerRoot, path));
   }

test/cloud_firestore_mocks_test.dart

@@ -492,6 +492,56 @@ void main() {
     final fooNameFirstName = fooName['firstName'] as String;
     expect(fooNameFirstName, 'Tomo');
   });
+
+  test('auto generate ID', () async {
+    final firestore = MockFirestoreInstance();
+    firestore.setupFieldValueFactory();
+
+    final reference1 = firestore.collection('users').document();
+    final document1Id = reference1.documentID;
+    final reference2 = firestore.collection('users').document();
+    expect(document1Id, isNot(reference2.documentID));
+
+    await reference1.setData({
+      'someField': 'someValue',
+    });
+    final snapshot1 = await reference1.get();
+    expect(snapshot1.exists, true);
+    // reference2 is not saved
+    final snapshot2 = await reference2.get();
+    expect(snapshot2.exists, false);
+
+    final snapshot =
+        await firestore.collection('users').document(document1Id).get();
+    expect(snapshot['someField'], 'someValue');
+
+    QuerySnapshot querySnapshot =
+        await firestore.collection('users').getDocuments();
+    // TODO: assert result length size. It should be 1.
+    // https://github.com/atn832/cloud_firestore_mocks/issues/20
+    expect(querySnapshot.documents.first['someField'], 'someValue');
+  });
+
+  test('Snapshot before saving data', () async {
+    final firestore = MockFirestoreInstance();
+    firestore.setupFieldValueFactory();
+
+    // These documents are not saved
+    final nonExistentId = 'salkdjfaarecikvdiko0';
+    final snapshot1 =
+        await firestore.collection('users').document(nonExistentId).get();
+    expect(snapshot1, isNotNull);
+    expect(snapshot1.documentID, nonExistentId);
+    // TODO: data field should be null before the document is saved
+    // https://github.com/atn832/cloud_firestore_mocks/issues/21
+    // expect(snapshot1.data, isNull);
+    expect(snapshot1.exists, false);
+
+    final snapshot2 = await firestore.collection('users').document().get();
+    expect(snapshot2, isNotNull);
+    expect(snapshot2.documentID.length, 20);
+    expect(snapshot2.exists, false);
+  });
 }
 
 class QuerySnapshotMatcher implements Matcher {