Can't correctly parse JSON fixture in tests - ruby-on-rails

Question

I'm using Test::Unit in an old Rails app (3.2.22) and I'm trying to test a service class that hits an external api.
I'm using webmock and trying to get a json file fixture working, but I keep getting parsing errors from the json file.
My test stub looks like this:
response_data = fixture_file_upload('easypost/order_response.json')
stub_request(:post, 'https://api.easypost.com/v2/orders').
to_return(:status => 200, :body => File.read(response_data))
My order_response.json file looks like this:
{
'mode':'test',
'reference':'Order',
'is_return':false,
'options':{'currency':'USD','label_date':null}
}
When I run the tests, I get a parse error:
JSON::ParserError: 757: unexpected token at '{'mode':'test','reference':'Order','is_return':false,'options':{'currency':'USD','label_date':null}}'
What is going on?
UPDATE:
Got it working by using double quotes in the JSON file:
{
"mode":"test",
"reference":"Order",
"is_return":false,
"options":{"currency":"USD","label_date":null}
}
Could anyone explain why this is necessary?

Answer 1

From the fine specification:
A string is a sequence of zero or more Unicode characters, wrapped in double quotes, using backslash escapes.
and and object is a set of key/value pairs where the keys are strings:
That means that this:
{
'mode':'test',
'reference':'Order',
'is_return':false,
'options':{'currency':'USD','label_date':null}
}
is not JSON because JSON strings use double quotes and only double quotes, that's just something that sort of looks like JSON. When you switch to double quotes for your strings:
{
"mode":"test",
"reference":"Order",
"is_return":false,
"options":{"currency":"USD","label_date":null}
}
then you have JSON and everything should work.

Answer 2

This is to make it simpler and to avoid having to have another escape method for javascript reserved keywords
I think this post might be helpful in understanding the need for quotations (and also where I found the above quote): JSON Spec - does the key have to be surrounded with quotes?