Essential App Case Study

Image Feed Feature Specs

Story: Customer requests to see their image feed

Narrative #1

As an online customer
I want the app to automatically load my latest image feed
So I can always enjoy the newest images of my friends

Scenarios (Acceptance criteria)

Given the customer has connectivity
 When the customer requests to see their feed
 Then the app should display the latest feed from remote
  And replace the cache with the new feed

Narrative #2

As an offline customer
I want the app to show the latest saved version of my image feed
So I can always enjoy images of my friends

Scenarios (Acceptance criteria)

Given the customer doesn't have connectivity
  And there’s a cached version of the feed
  And the cache is less than seven days old
 When the customer requests to see the feed
 Then the app should display the latest feed saved

Given the customer doesn't have connectivity
  And there’s a cached version of the feed
  And the cache is seven days old or more
 When the customer requests to see the feed
 Then the app should display an error message

Given the customer doesn't have connectivity
  And the cache is empty
 When the customer requests to see the feed
 Then the app should display an error message

Use Cases

Load Feed From Remote Use Case

Data:

Primary course (happy path):

Invalid data – error course (sad path):

No connectivity – error course (sad path):

Load Feed Image Data From Remote Use Case

Data:

Primary course (happy path):

Cancel course:

Invalid data – error course (sad path):

No connectivity – error course (sad path):

Load Feed From Cache Use Case

Primary course:

Retrieval error course (sad path):

Expired cache course (sad path):

Empty cache course (sad path):

Load Feed Image Data From Cache Use Case

Data:

Primary course (happy path):

Cancel course:

Retrieval error course (sad path):

Empty cache course (sad path):

Validate Feed Cache Use Case

Primary course:

Retrieval error course (sad path):

Expired cache course (sad path):

Cache Feed Use Case

Data:

Primary course (happy path):

Deleting error course (sad path):

Saving error course (sad path):

Cache Feed Image Data Use Case

Data:

Primary course (happy path):

Saving error course (sad path):

Flowchart

Model Specs

Feed Image

Payload contract

GET /feed

200 RESPONSE

{
	"items": [
		{
			"id": "a UUID",
			"description": "a description",
			"location": "a location",
			"image": "https://a-image.url",
		},
		{
			"id": "another UUID",
			"description": "another description",
			"image": "https://another-image.url"
		},
		{
			"id": "even another UUID",
			"location": "even another location",
			"image": "https://even-another-image.url"
		},
		{
			"id": "yet another UUID",
			"image": "https://yet-another-image.url"
		}
		...
	]
}

Image Comments Feature Specs

Story: Customer requests to see image comments

Narrative

As an online customer
I want the app to load image commments
So I can see how people are engaging with images in my feed

Scenarios (Acceptance criteria)

Given the customer has connectivity
 When the customer requests to see comments on an image
 Then the app should display all comments for that image

Given the customer doesn't have connectivity
 When the customer requests to see comments on an image
 Then the app should display an error message

Use Cases

Load Image Comments From Remote Use Case

Data:

Primary course (happy path):

Invalid data – error course (sad path):

No connectivity – error course (sad path):

Model Specs

Image Comment

Image Comment Author

Payload contract

GET /image/{image-id}/comments

2xx RESPONSE

{
	"items": [
		{
			"id": "a UUID",
			"message": "a message",
			"created_at": "2020-05-20T11:24:59+0000",
			"author": {
				"username": "a username"
			}
		},
		{
			"id": "another UUID",
			"message": "another message",
			"created_at": "2020-05-19T14:23:53+0000",
			"author": {
				"username": "another username"
			}
		},
		...
	]
}

App Architecture