First tests & JSON – Github linter

Our bot will be working with JSON data. So we can learn some fancy things today:

Types

Everything is a type. A strong type. No exception in JSON. GitHub’s JSON format is known. So we can convert string representation to instance of type.

In PureScript there’re types, datas & records. As far as I know. We must use data in case of decoding JSON. Probably future will tell us why :)

First let’s define type:

data PushEvent = PushEvent {
  ref :: String
}

Our first test - read & test ref property.

Unit testing

Pulp itself has pulp test command which runs tests from Test folder. This folder can be used as a battlefield as well :)

We need some assertion library - basic purescript-assert is enough.

Which points us to JSON.

Test data

To parse JSON we will use purescript-foreign package. After installation we can test it using pulp test.

But first we should have some data to work with. Fortunately for us GitHub provides example of PushEvent which will be sent by GitHub when Push happened to repository.

Lets download it and save into Test/push_event.json.

Now we should read it :) There’s a wrapper for Node’s FS module - purescript-node-fs. We will use it.

getPushEventFromJSON = do
  content <- readTextFile UTF8 "test/push_event.json"
  return $ readJSON content :: F PushEvent

Simple - bind contents of “test/push_event.json” file to content. More about bind in future episodes :) Next - parse JSON into proper object - PushEvent.

There’s however one gotcha - the result is an either type. We’ll need to handle it differently.

Assert

Let’s write our main function:

1
2
3
4
5
6
7
8 checkParsedMessage p =
  p.ref == "refs/heads/changes"

main = do
  push_event <- getPushEventFromJSON
  case push_event of
    Right (PushEvent p) -> assert' "Wrong value after parsing!" $ checkParsedMessage p
    Left  _ -> assert' "Error during decoding" false

As we can see in line 5 - bind either value from parsed file into push_event name. Next line - match both paths - happy path (Right - as “right is right”) and left. If we have Left - then there’s an error and we must fail - assert false is enough. For right value - let’s write helper function that’ll do checking for us.

Let’s run it:

$ pulp test
* Build successful.
* Running tests...
* Tests OK.

Success! Code as always it it’s tag