How to test JSON result from Ruby on Rails functional tests?

In Rails >= 5

Use ActionDispatch::TestResponse#parsed_body.

Example:

user = @response.parsed_body
assert_equal "Mike", user['name']

In Rails up to 4.x

Use JSON.parse, which takes a string as input and returns a Ruby hash that the JSON represents.

Example:

user = JSON.parse(@response.body)
assert_equal "Mike", user['name']

If you are using RSpec, json_spec is worth a look

https://github.com/collectiveidea/json_spec

Rails has JSON support built in:

def json_response
    ActiveSupport::JSON.decode @response.body
end

No need for a plugin

Then you can do something like this:

assert_equal "Mike", json_response['name']

Also for short JSON responses you can simply match a string of the JSON to @response.body. This prevents having to rely on yet another gem.

assert_equal '{"total_votes":1}', @response.body