Add comments from PR and change S3 key format

__mocks__/cognito-fake.js

@@ -1,3 +1,4 @@
+// Yes, this is gross, but this is the interface of the dependency we're faking.
 export default class CognitoFake {
   listUsers() {
     return {

__mocks__/cognito-pagination-fake.js

@@ -1,5 +1,9 @@
+// Yes, this is gross, but this is the interface of the dependency we're faking.
+
 export default class CognitoPaginationFake {
   constructor() {
+    // This attr makes sure we can split a result set into paginated chunks
+    // without endless recursion.
     this.calledAlready = false
   }
 

__tests__/CopyUsers.test.js

@@ -19,7 +19,7 @@ describe('CopyUsers', () => {
     })
     it('sets objectKey', () => {
       // Matches: {ISO DATE}/{AWS_REGION}_{USER_POOL_ID}.json
-      expect(copier.objectKey).toMatch(/\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d+Z\/my-region-1_uSeRPoOlId\.json/)
+      expect(copier.objectKey).toMatch(/\d{4}-\d{2}-\d{2}\/user-backup_\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d+Z_my-region-1_uSeRPoOlId\.json/)
     })
   })
 
@@ -38,6 +38,8 @@ describe('CopyUsers', () => {
         expect(s3Spy).toHaveBeenCalledWith({
           Body: "[{\"Username\":\"user1\"},{\"Username\":\"user2\"}]",
           Bucket: 'my-bucket-name',
+          // The key value includes an ISO representation of a timestamp, so
+          // without gnarly date/time mocking, this is the best I could do here.
           Key: expect.any(String)
         }, expect.any(Function))
         expect(logSpy).toHaveBeenCalledWith('Users backed up to S3')

src/CopyUsers.js

@@ -7,7 +7,9 @@ export default class CopyUsers {
     AWS.config = configureAWS(AWS.config)
     this.userListString = JSON.stringify(userList)
     this.s3 = new AWS.S3()
-    this.objectKey = `${new Date().toISOString()}/${config.get('userPoolId')}.json`
+    const timestamp = new Date().toISOString()
+    const datestamp = timestamp.slice(0, 10)
+    this.objectKey = `${datestamp}/user-backup_${timestamp}_${config.get('userPoolId')}.json`
   }
 
   copy() {