JSON Assertions

Ruby Gem providing assert methods useful for validate JSON documents during API development. It also supports extracting JSON values using a path syntax.

Usage

Add to your Gemfile.

group :test do
  gem "json_assertions"
end

The module expects response.body method to available where ever it is included. It should work with Rails just fine but if your framework does not provide response.body then just create a json_response method to return parsed JSON. There should also be an assert method available.

Example

# Rails 5
require 'test_helper'

class UsersControllerTest < ActionDispatch::IntegrationTest

  include JsonAssertions

  test "index returns array of users item" do
    get "/users"
  
    assert_json_is_array '/users'
    assert_json_array_size 10, '/users'
    assert_json_equal 123, '/users/0/id'
    assert_json_has '/users/0/created_at'
    assert_json_equal "John Doe", '/users/0/name'
  
    # alternative syntax
    with_json response.body do |json|
      json.array_size_is 10 '/users'
      json.must_have '/users/0/id'
      json.must_not_have '/users/0/password'
      json.array_map_equals [123,456,789], '/users', '/id'
      json.equal 'John Doe', '/users/0/name'
      assert_equal 123, json["users"]["id"]
    end
  end
end

Documentation

There is a simple syntax for the JSON path which is just the series of keys joined with a slash /. For example, with {"users": [{"id": 123, "name": "John"}]} using path /users/0/id would return 123.

Generic Helpers

• puts pretty_json(response.body)

Available Assertions

• assert_json_equal(expected, path, message=nil)
• assert_json_match(regex, path, message=nil)
• assert_json_missing(path, message=nil)
• assert_json_has(path, message=nil)
• assert_json_array_size(expected, path, message=nil)
• assert_json_is_array(path, message=nil)

Assertions availabe when using with_json(response.body){|j| }

• [](key)
• equal(expected, path, message=nil)
• matches(regex, path, message)
• must_have(path, message=nil)
• must_not_have(path, message=nil)
• array_size_gte(expected_size, path, message=nil)
• array_size_is(expected_size,path, message=nil)
• array_length_is(expected_size, path, message=nil)
• array_map_equals(expected_list, list_path, value_path, message=nil)
• is_array?(path, message=nil)
• value_at(path, message=nil)

If the assertions fails, the error message will output a pretty version of the response JSON which has been modified to only include nessisary details which is helpful when working with large JSON structures.

1) Failure:
JsonAssertionsTest#test_with_json:
JSON path /users/1/name exists but expected to be missing.
{
  "users": [
    {
      "__additional keys__": [
        "id",
        "name"
      ]
    },
    "... (2 total) ..."
  ]
}

Contribute

Contributions are welcome. Just create a fork and create a PR.