json_expressions

by chancancode

chancancode / json_expressions

JSON matchmaking for all your API testing needs.

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JSON Expressions

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Introduction

Your API is a contract between your service and your developers. It is important for you to know exactly what your JSON API is returning to the developers in order to make sure you don't accidentally change things without updating the documentations and/or bumping the API version number. Perhaps some controller tests for your JSON endpoints would help:

# MiniTest::Unit example
class UsersControllerTest < MiniTest::Unit::TestCase
  def test_get_a_user
    server_response = get '/users/chancancode.json'

json = JSON.parse server_response.body

assert user = json['user']

assert user_id = user['id']
assert_equal 'chancancode', user['username']
assert_equal 'Godfrey Chan', user['full_name']
assert_equal '[email protected]', user['email']
assert_equal 'Administrator', user['type']
assert_kind_of Integer, user['points']
assert_match /\Ahttps?\:\/\/.*\z/i, user['homepage']

assert posts = user['posts']

assert_kind_of Integer, posts[0]['id']
assert_equal 'Hello world!', posts[0]['subject']
assert_equal user_id, posts[0]['user_id']
assert_include posts[0]['tags'], 'announcement'
assert_include posts[0]['tags'], 'welcome'
assert_include posts[0]['tags'], 'introduction'

assert_kind_of Integer, posts[1]['id']
assert_equal 'An awesome blog post', posts[1]['subject']
assert_equal user_id, posts[1]['user_id']
assert_include posts[0]['tags'], 'blog'
assert_include posts[0]['tags'], 'life'

end end

There are many problems with this approach of JSON matching:

  • It could get out of hand really quickly
  • It is not very readable
  • It flattens the structure of the JSON and it's difficult to visualize what the JSON actually looks like
  • It does not guard against extra parameters that you might have accidentally included (password hashes, credit card numbers etc)
  • Matching nested objects and arrays is tricky, especially when you don't want to enforce a particular ordering of the returned objects

json_expression allows you to express the structure and content of the JSON you're expecting with very readable Ruby code while preserving the flexibility of the "manual" approach.

Dependencies

  • Ruby 1.9+

Usage

Add it to your Gemfile:

gem 'json_expressions'

Add this to your test/spec helper file: ```ruby

For MiniTest::Unit

require 'json_expressions/minitest'

For RSpec

require 'json_expressions/rspec' ```

Which allows you to do... ```ruby

MiniTest::Unit example

class UsersControllerTest < MiniTest::Unit::TestCase def testgetauser serverresponse = get '/users/chancancode.json'

# This is what we expect the returned JSON to look like
pattern = {
  user: {
    id:         :user_id,                    # "Capture" this value for later
    username:   'chancancode',               # Match this exact string
    full_name:  'Godfrey Chan',
    email:      '[email protected]',
    type:       'Administrator',
    points:     Integer,                     # Any integer value
    homepage:   /\Ahttps?\:\/\/.*\z/i,       # Let's get serious
    created_at: wildcard_matcher,            # Don't care as long as it exists
    updated_at: wildcard_matcher,
    posts: [
      {
        id:      Integer,
        subject: 'Hello world!',
        user_id: :user_id,                   # Match against the captured value
        tags: [
          'announcement',
          'welcome',
          'introduction'
        ]                                    # Ordering of elements does not matter by default
      }.ignore_extra_keys!,                  # Skip the uninteresting stuff
      {
        id:      Integer,
        subject: 'An awesome blog post',
        user_id: :user_id,
        tags:    ['blog' , 'life']
      }.ignore_extra_keys!
    ].ordered!                               # Ensure the posts are in this exact order
  }
}

matcher = assert_json_match pattern, server_response.body # Returns the Matcher object

You can use the captured values for other purposes

assert matcher.captures[:user_id] > 0

end end

MiniTest::Spec example

describe UsersController, "#show" do it "returns a user" do pattern = # See above...

server_response = get '/users/chancancode.json'

server_response.body.must_match_json_expression(pattern)

end end

RSpec example

describe UsersController, "#show" do it "returns a user" do pattern = # See above...

server_response = get '/users/chancancode.json'

server_response.body.should match_json_expression(pattern)

end end ```

Basic Matching

This pattern

ruby
{
  integer: 1,
  float:   1.1,
  string:  'Hello world!',
  boolean: true,
  array:   [1,2,3],
  object:  {key1: 'value1',key2: 'value2'},
  null:    nil,
}
matches the JSON object
json
{
  "integer": 1,
  "float": 1.1,
  "string": "Hello world!",
  "boolean": true,
  "array": [1,2,3],
  "object": {"key1": "value1", "key2": "value2"},
  "null": null
}

Wildcard Matching

You can use

wildcard_matcher
to ignore keys that you don't care about (other than the fact that they exist).

This pattern

ruby
[ wildcard_matcher, wildcard_matcher, wildcard_matcher, wildcard_matcher, wildcard_matcher, wildcard_matcher, wildcard_matcher ]
matches the JSON array
json
[ 1, 1.1, "Hello world!", true, [1,2,3], {"key1": "value1","key2": "value2"}, null]

Furthermore, because the pattern is just plain old Ruby code, you can also write:

ruby
[ wildcard_matcher ] * 7

Note: Previously, the examples here uses

WILDCARD_MATCHER
which is a constant defined on
MiniTest::Unit::TestCase
. Since 0.8.0, the use of this constant is discouraged because it doesn't work for
MiniTest::Spec
and
RSpec
due to how Ruby scoping works for blocks. Instead,
wildcard_matcher
(a method) has been added. This is now the preferred way to retrieve the wildcard matcher in order to maintain consistency among the different test frameworks.

Object Equality

By default, jsonexpressions uses

Object#===
to match against the corresponding value in the target JSON. In most cases, this method behaves exactly the same as
Object#==
. However, certain classes override this method to provide specialized behavior (notably
Regexp
,
Module
and
Range
, see below). If you find this undesirable for certain classes, you can explicitly opt them out and json
expressions will call

Object#==
instead:
# This is the default setting
JsonExpressions::Matcher.skip_triple_equal_on = [ ]

To add more modules/classes

JsonExpressions::Matcher.skip_triple_equal_on << MyClass

To turn this off completely

JsonExpressions::Matcher.skip_triple_equal_on = [ BasicObject ]

Regular Expressions

Since

Regexp
overrides
Object#===
to mean "matches", you can use them in your patterns and json_expressions will do the right thing:
ruby
{ hex: /\A0x[0-9a-f]+\z/i }
matches
json
{ "hex": "0xC0FFEE" }
but not
json
{ "hex": "Hello world!" }

Type Matching

Module
(and by inheritance,
Class
) overrides
===
to mean
instance of
. You can exploit this behavior to do type matching:
ruby
{
  integer: Integer,
  float:   Float,
  string:  String,
  boolean: Boolean, # See http://stackoverflow.com/questions/3028243/check-if-ruby-object-is-a-boolean#answer-3028378
  array:   Array,
  object:  Hash,
  null:    NilClass,
}
matches the JSON object
json
{
  "integer": 1,
  "float": 1.1,
  "string": "Hello world!",
  "boolean": true,
  "array": [1,2,3],
  "object": {"key1": "value1", "key2": "value2"},
  "null": null
}

Ranges

Range
overrides
===
to mean
include?
. Therefore,
ruby
{ day: (1..31), month: (1..12) }
matches the JSON object
json
{ "day": 3, "month": 11 }
but not
json
{ "day": -1, "month": 13 }

This is also helpful for comparing Floats to a certain precision.

ruby
{ pi: 3.141593 }
won't match
json
{ "pi": 3.1415926536 }
But this will:
ruby
{ pi: (3.141592..3.141593) }

Capturing

Similar to how "captures" work in Regexp, you can capture the value of certain keys for later use: ```ruby matcher = JsonExpressions::Matcher.new({ key1: :key1, key2: :key2, key3: :key3 })

matcher =~ JSON.parse('{"key1":"value1", "key2":"value2", "key3":"value3"}') # => true

matcher.captures[:key1] # => "value1" matcher.captures[:key2] # => "value2" matcher.captures[:key3] # => "value3" ```

If the same symbol is used multiple times, jsonexpression will make sure they agree. This pattern ```ruby { key1: :captureme, key2: :captureme, key3: :captureme }

matches
json { "key1": "Hello world!", "key2": "Hello world!", "key3": "Hello world!" }
but not
json { "key1": "value1", "key2": "value2", "key3": "value3" } ```

Ordering

By default, all arrays and JSON objects (i.e. Ruby hashes) are assumed to be unordered. This means

ruby
[ 1, 2, 3, 4, 5 ]
will match
json
[ 5, 3, 2, 1, 4 ]
and
ruby
{ key1: 'value1', key2: 'value2' }
will match
json
{ "key2": "value2", "key1": "value1" }

You can change this behavior in a case-by-case manner:

ruby
{
  unordered_array: [1,2,3,4,5].unordered!, # calling unordered! is optional as it's the default
  ordered_array:   [1,2,3,4,5].ordered!,
  unordered_hash:  {a: 1, b: 2}.unordered!,
  ordered_hash:    {a: 1, b: 2}.ordered!
}

Or you can change the defaults: ```ruby

Default for these are true

JsonExpressions::Matcher.assumeunorderedarrays = false JsonExpressions::Matcher.assumeunorderedhashes = false ```

"Strictness"

By default, all arrays and JSON objects (i.e. Ruby hashes) are assumed to be "strict". This means any extra elements or keys in the JSON target will cause the match to fail:

ruby
[ 1, 2, 3, 4, 5 ]
will not match
json
[ 1, 2, 3, 4, 5, 6 ]
and
ruby
{ key1: 'value1', key2: 'value2' }
will not match
json
{ "key1": "value1", "key2": "value2", "key3": "value3" }

You can change this behavior in a case-by-case manner:

ruby
{
  strict_array:    [1,2,3,4,5].strict!, # calling strict! is optional as it's the default
  forgiving_array: [1,2,3,4,5].forgiving!,
  strict_hash:     {a: 1, b: 2}.strict!,
  forgiving_hash:  {a: 1, b: 2}.forgiving!
}

They also come with some more sensible aliases:

ruby
{
  strict_array:    [1,2,3,4,5].reject_extra_values!,
  forgiving_array: [1,2,3,4,5].ignore_extra_values!,
  strict_hash:     {a: 1, b: 2}.reject_extra_keys!,
  forgiving_hash:  {a: 1, b: 2}.ignore_extra_keys!
}

Or you can change the defaults: ```ruby

Default for these are true

JsonExpressions::Matcher.assumestrictarrays = false JsonExpressions::Matcher.assumestricthashes = false ```

Support for other test frameworks

The

Matcher
class itself is written in a framework-agnostic manner. This allows you to easily write custom helpers/matchers for your favorite testing framework. If you wrote an adapter for another test frameworks and you'd like to share yhat with the world, please open a Pull Request.

Contributing

Please use the GitHub issue tracker for bugs and feature requests. If you could submit a pull request - that's even better!

License

This library is distributed under the MIT license. Please see the LICENSE file.

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