has_only: enforce a fixed sets of JSON object properties

README.md

@@ -58,6 +58,26 @@ assert_json '[{"id":1, "key":"test", "name":"test"}, {"id":2, "key":"test", "nam
 end
 ```
 
+To test that objects have the declared set of properties and nothing more,
+include `has_only` at any level, like this
+
+```ruby
+assert_json '[{"id":1, "key":"test", "name":"test"}, {"id":2, "key":"test", "name":"test"}, {"id":3, "key":"test", "name":"test"}]' do
+  has_only
+  item 0 do
+    has :id, 1
+    has :key, 'test'
+    has :name, 'test'
+  end
+  item 1 do
+    has 'id', 2
+    has 'key', 'test'
+  end
+end
+
+# Failure: element 1 has unexpected keys: name
+```
+
 
 ## Changelog ##
 

lib/assert_json/assert_json.rb

@@ -5,6 +5,7 @@ def assert_json(json_string, &block)
       @json = AssertJson::Json.new(json_string)
       # json.instance_exec(json, &block)
       yield @json
+      @json.test_for_unexpected_keys('root')
     end
   end
 
@@ -20,19 +21,31 @@ def has_not(*args, &block)
     @json.has_not(*args, &block)
   end
 
+  def has_only
+    @json.has_only
+  end
+
   class Json
 
     def initialize(json_string)
       @decoded_json = ActiveSupport::JSON.decode(json_string)
+      @expected_keys = []
+      @only = false
     end
 
     def item(index, &block)
+      only_in_scope = @only
+      expected_keys_in_scope = @expected_keys
+      @expected_keys = []
       decoded_json_in_scope = @decoded_json
       @decoded_json = @decoded_json[index]
       begin
         yield if block_given?
+        test_for_unexpected_keys(index)
       ensure
         @decoded_json = decoded_json_in_scope
+        @expected_keys = expected_keys_in_scope
+        @only = only_in_scope
       end
     end
 
@@ -79,8 +92,13 @@ def element(*args, &block)
         flunk
       end
 
+      @expected_keys.push arg
+
       if block_given?
         begin
+          only_in_scope = @only
+          expected_keys_in_scope = @expected_keys
+          @expected_keys = []
           decoded_json_in_scope = @decoded_json
           @decoded_json = case token
                           when Hash
@@ -89,11 +107,13 @@ def element(*args, &block)
                             token
                           end
           yield
+          test_for_unexpected_keys(arg)
         ensure
+          @expected_keys = expected_keys_in_scope
+          @only = only_in_scope
           @decoded_json = decoded_json_in_scope
         end
       end
-
     end
     alias has element
 
@@ -109,6 +129,22 @@ def not_element(*args, &block)
     end
     alias has_not not_element
 
+    def only
+      @only = true
+    end
+    alias has_only only
+
+    def test_for_unexpected_keys(name = 'root')
+      return unless @only
+
+      if @decoded_json.is_a?(Hash)
+        unexpected_keys = @decoded_json.keys - @expected_keys
+        if unexpected_keys.count > 0
+          raise_error("element #{name} has unexpected keys: #{unexpected_keys.join(', ')}")
+        end
+      end
+    end
+
     private
 
       def raise_error(message)

test/assert_json_has_only_test.rb

@@ -0,0 +1,94 @@
+require_relative './test_helper'
+
+class AssertJsonHasNoUnexpectedKeysTest < Minitest::Test
+  include AssertJson
+
+  def test_on_root_object
+    assert_json '{"keyA":"value","keyB":"value"}' do
+      has_only
+      has 'keyA'
+      has 'keyB'
+    end
+  end
+
+  def test_on_root_object_failure
+    err = assert_raises(MiniTest::Assertion) do
+      assert_json '{"keyA":"value","keyB":"value"}' do
+        has_only
+        has 'keyA', 'value'
+      end
+    end
+    assert_equal 'element root has unexpected keys: keyB', err.message
+  end
+
+  def test_on_root_object_with_sub_object
+    assert_json '{"keyA":{"subKeyA":"value","subKeyB":"value"},"keyB":"value"}' do
+      has_only
+      has 'keyA' do
+        has 'subKeyA'
+        has 'subKeyB'
+      end
+      has 'keyB'
+    end
+  end
+
+  def test_on_root_object_with_sub_object_failure
+    err = assert_raises(MiniTest::Assertion) do
+      assert_json '{"keyA":{"subKeyA":"value","subKeyB":"value"},"keyB":"value"}' do
+        has_only
+        has 'keyA' do
+          has 'subKeyA'
+          has 'subKeyB'
+        end
+      end
+    end
+    assert_equal 'element root has unexpected keys: keyB', err.message
+  end
+
+  def test_on_sub_object
+    assert_json '{"keyA":{"subKeyA":"value","subKeyB":"value"},"keyB":"value"}' do
+      has 'keyA' do
+        has_only
+        has 'subKeyA'
+        has 'subKeyB'
+      end
+    end
+  end
+
+  def test_on_sub_object_failure
+    err = assert_raises(MiniTest::Assertion) do
+      assert_json '{"keyA":{"subKeyA":"value","subKeyB":"value"},"keyB":"value"}' do
+        has 'keyA' do
+          has_only
+          has 'subKeyA'
+        end
+      end
+    end
+    assert_equal 'element keyA has unexpected keys: subKeyB', err.message
+  end
+
+  def test_on_root_array_of_objects
+    assert_json '[{"id":1, "key":"test", "name":"test"}, {"id":2, "key":"test", "name":"test"}, {"id":3, "key":"test", "name":"test"}]' do
+      has_only
+      item 0 do
+        has :id, 1
+        has :key, 'test'
+        has :name, 'test'
+      end
+    end
+  end
+
+  def test_on_root_array_of_objects_failure
+    err = assert_raises(MiniTest::Assertion) do
+      assert_json '[{"id":1, "key":"test", "name":"test"}, {"id":2, "key":"test", "name":"test"}, {"id":3, "key":"test", "name":"test"}]' do
+        has_only
+        item 0 do
+          has :id, 1
+          has :key, 'test'
+        end
+      end
+    end
+    assert_equal 'element 0 has unexpected keys: name', err.message
+  end
+
+end