add unit test for withRevCheck method

services/docstore/app/js/MongoManager.js

@@ -15,7 +15,7 @@ const { db, ObjectId } = require('./mongodb')
 const logger = require('logger-sharelatex')
 const metrics = require('@overleaf/metrics')
 const Settings = require('@overleaf/settings')
-const { DocModifiedError } = require('./Errors')
+const Errors = require('./Errors')
 const { promisify } = require('util')
 
 module.exports = MongoManager = {
@@ -206,7 +206,7 @@ module.exports = MongoManager = {
         if (err) return callback(err)
         if (doc.rev !== currentRev) {
           return callback(
-            new DocModifiedError('doc rev has changed', {
+            new Errors.DocModifiedError('doc rev has changed', {
               doc_id: doc._id,
               rev: doc.rev,
               currentRev,

services/docstore/test/unit/js/MongoManagerTests.js

@@ -29,7 +29,7 @@ describe('MongoManager', function () {
         },
         '@overleaf/metrics': { timeAsyncMethod: sinon.stub() },
         '@overleaf/settings': { max_deleted_docs: 42 },
-        './Errors': { Errors },
+        './Errors': Errors,
       },
     })
     this.project_id = ObjectId().toString()
@@ -307,7 +307,7 @@ describe('MongoManager', function () {
     })
   })
 
-  return describe('setDocVersion', function () {
+  describe('setDocVersion', function () {
     beforeEach(function () {
       this.version = 42
       this.db.docOps.updateOne = sinon.stub().callsArg(3)
@@ -340,4 +340,36 @@ describe('MongoManager', function () {
       return this.callback.called.should.equal(true)
     })
   })
+
+  describe('withRevCheck', function () {
+    this.beforeEach(function () {
+      this.doc = { _id: ObjectId(), name: 'mock-doc', rev: 1 }
+      this.testFunction = sinon.stub().yields(null, 'foo')
+    })
+
+    it('should call the callback when the rev has not changed', function (done) {
+      this.db.docs.findOne = sinon.stub().callsArgWith(2, null, { rev: 1 })
+      this.MongoManager.withRevCheck(
+        this.doc,
+        this.testFunction,
+        (err, result) => {
+          result.should.equal('foo')
+          assert.isNull(err)
+          done()
+        }
+      )
+    })
+
+    it('should return an error when the rev has changed', function (done) {
+      this.db.docs.findOne = sinon.stub().callsArgWith(2, null, { rev: 2 })
+      this.MongoManager.withRevCheck(
+        this.doc,
+        this.testFunction,
+        (err, result) => {
+          err.should.be.instanceof(Errors.DocModifiedError)
+          done()
+        }
+      )
+    })
+  })
 })