jest-json


Jest matchers to work with JSON strings.

Setup

Note: If you're using Jest < 27.2.5, you should stick to jest-json@^1.0.

Add jest-json to your Jest config:

``json
{
"setupTestFrameworkScriptFile": "jest-json"
}
`

Or if you're already using another test framework, create a setup file and require each of them:

`js
require("jest-json");
// require("some-jest-library);
`

Motivation

Say you need to assert foo was called with foo("url", "{'foo': 'bar', 'spam': 'eggs'}"):

`js
// option 1
expect(foo).toHaveBeenCalledWith(
"url",
JSON.stringify({
foo: "bar",
spam: "eggs",
})
);
`

This test may fail depending on how the second argument was created:

`js
// this will pass the test:
foo(
"url",
JSON.stringify({
foo: "bar",
spam: "eggs",
})
);

// this will fail the test:
foo(
"url",
JSON.stringify({
spam: "eggs",
foo: "bar",
})
);
`

_See this repl.it for a working example._

To fix the test you'd have to find in foo.mock.calls the call you want, parse the JSON and call expect().toEqual({ spam: "eggs", foo: "bar" }).

Matchers

$3

In the example above, you can use the expect.jsonMatching asymmetric matcher:

`js
expect(foo).toHaveBeenCalledWith(
"url",
expect.jsonMatching({
foo: "bar",
spam: "eggs",
})
);
`

You can include other asymmetric matchers inside like:


`js
expect.jsonMatching(
expect.objectContaining({
foo: expect.stringMatching("bar")
})
)
`

$3

It's just sugar for calling JSON.parse() and then expect().toEqual():

`js
expect(json).toMatchJSON(expected);
// equivalent to:
const tmp = JSON.parse(json);
expect(tmp).toEqual(expected);
``