Add match_json for exact matching of JSON

This commit adds a `match_json` matcher which only succeeds when the
value being tested has *exactly* the fields specified.

The work here was partly based on waterlink#39.

Author: matthew-healy

features/rspec/json_expectations/match_json.feature

@@ -0,0 +1,139 @@
+Feature: match_json matcher
+
+  As a developer writing expectations against JSON with RSpec
+  I want to be able to match against the exact structure of a JSON object
+  So I have confidence no additional fields are included
+
+  Background:
+    Given a file "spec/spec_helper.rb" with:
+          """ruby
+          require "rspec/json_expectations"
+          """
+    And a local "SIMPLE_HASH" with:
+          """ruby
+          {
+            id: 25,
+            email: "[email protected]",
+            name: "John"
+          }
+          """
+    And a local "SIMPLE_JSON" with:
+          """json
+          {
+            "name": "Matthew",
+            "age": 33
+          }
+          """
+    And a local "NESTED_JSON" with:
+          """json
+          {
+            "nested": {
+              "a": 1,
+              "b": 2
+            }
+          }
+          """
+          
+    
+
+  Scenario: Correctly expecting hash to include simple json
+    Given a file "spec/simple_example_spec.rb" with:
+          """ruby
+          require "spec_helper"
+
+          RSpec.describe "A json response" do
+            subject { %{SIMPLE_HASH} }
+
+            it "has basic info about user" do
+              expect(subject).to match_json(
+                id: 25,
+                email: "[email protected]",
+                name: "John"
+              )
+            end
+          end
+          """
+    When I run "rspec spec/simple_example_spec.rb"
+    Then I see:
+          """
+          1 example, 0 failures
+          """
+
+  Scenario: Wrongly expecting hash to include simple json
+    Given a file "spec/simple_with_fail_spec.rb" with:
+          """ruby
+          require "spec_helper"
+
+          RSpec.describe "A json response" do
+            subject { %{SIMPLE_HASH} }
+
+            it "has basic info about user" do
+              expect(subject).to match_json(
+                id: 25,
+                email: "[email protected]",
+              )
+            end
+          end
+          """
+    When I run "rspec spec/simple_with_fail_spec.rb"
+    Then I see:
+          """
+          1 example, 1 failure
+          """
+    And I see:
+          """
+                             expected: {id: 25, email: "[email protected]"}
+                                  got: {id: 25, email: "[email protected]", name: "John"}
+          """
+
+  Scenario: Wrongly expecting JSON string to include simple JSON
+    Given a file "spec/json_string_with_fail_spec.rb" with:
+          """ruby
+          require "spec_helper"
+
+          RSpec.describe "test" do
+            subject { '%{SIMPLE_JSON}' }
+
+            it "passes" do
+              expect(subject).to match_json(name: "Matthew")
+            end
+          end
+          """
+    When I run "rspec spec/json_string_with_fail_spec.rb"
+    Then I see:
+          """
+          1 example, 1 failure
+          """
+    And I see:
+          """
+                             expected: {name: "Matthew"}
+                                  got: {"name" => "Matthew", "age" => 33}
+          """
+
+  Scenario: Wrongly expecting JSON string to include nested JSON
+    Given a file "spec/fail_in_nested_json.rb" with:
+          """ruby
+          require "spec_helper"
+
+          RSpec.describe "test" do
+            subject { '%{NESTED_JSON}' }
+
+            it "passes" do
+              expect(subject).to match_json(nested: {a: 1})
+            end
+          end
+          """
+    When I run "rspec spec/fail_in_nested_json.rb"
+    Then I see:
+          """
+          1 example, 1 failure
+          """
+    And I see:
+          """
+                           json atom at path "nested" is not equal to expected value:
+          """
+    And I see:
+          """
+                             expected: {a: 1}
+                                  got: {"a" => 1, "b" => 2}
+          """

lib/rspec/json_expectations/json_traverser.rb

@@ -16,7 +16,7 @@ class JsonTraverser
       class << self
         def traverse(errors, expected, actual, negate=false, prefix=[], options={})
           [
-            handle_hash(errors, expected, actual, negate, prefix),
+            handle_hash(errors, expected, actual, negate, prefix, options),
             handle_array(errors, expected, actual, negate, prefix),
             handle_unordered(errors, expected, actual, negate, prefix, options),
             handle_value(errors, expected, actual, negate, prefix),
@@ -28,22 +28,27 @@ def traverse(errors, expected, actual, negate=false, prefix=[], options={})
 
         private
 
-        def handle_keyvalue(errors, expected, actual, negate=false, prefix=[])
+        def handle_keyvalue(errors, expected, actual, negate=false, prefix=[], options={})
+          if options[:exact_size] && expected.size != actual.size
+            errors[prefix.join("/")] = {expected:, actual:}
+            return conditionally_negate(false, negate)
+          end
+
           expected.map do |key, value|
             new_prefix = prefix + [key]
             if has_key?(actual, key)
-              traverse(errors, value, fetch(actual, key), negate, new_prefix)
+              traverse(errors, value, fetch(actual, key), negate, new_prefix, options)
             else
               errors[new_prefix.join("/")] = :no_key unless negate
               conditionally_negate(false, negate)
             end
           end.all? || false
         end
 
-        def handle_hash(errors, expected, actual, negate=false, prefix=[])
+        def handle_hash(errors, expected, actual, negate=false, prefix=[], options={})
           return nil unless expected.is_a?(Hash)
 
-          handle_keyvalue(errors, expected, actual, negate, prefix)
+          handle_keyvalue(errors, expected, actual, negate, prefix, options)
         end
 
         def handle_array(errors, expected, actual, negate=false, prefix=[])

lib/rspec/json_expectations/matchers.rb

@@ -21,6 +21,27 @@ def traverse(expected, actual, negate=false)
   end
 end
 
+RSpec::JsonExpectations::MatcherFactory.new(:match_json).define_matcher do
+  def traverse(expected, actual, negate=false)
+    supported_types = [Hash, Array, ::RSpec::JsonExpectations::Matchers::UnorderedArrayMatcher]
+
+    unless supported_types.any? { expected.is_a?(it) }
+      raise ArgumentError, "Expected value in match_json must be JSON-ish"
+    end
+
+    representation = actual.is_a?(String) ? JSON.parse(actual) : actual
+
+    RSpec::JsonExpectations::JsonTraverser.traverse(
+      @include_json_errors = { _negate: negate},
+      expected,
+      representation,
+      negate,
+      [],
+      {exact_size: true}
+    )
+  end
+end
+
 RSpec::JsonExpectations::MatcherFactory.new(:include_unordered_json).define_matcher do
   def traverse(expected, actual, negate=false)
     unless expected.is_a?(Array)