add Publishing API test helpers for /schemas

`/schemas` and `/schemas/{schema_name}` were added
to the Publishing API in this PR [1].

This adds helper methods to stub responses to these
end points.

[1] alphagov/publishing-api#2767

lib/gds_api/test_helpers/publishing_api.rb

@@ -802,6 +802,59 @@ def stub_publishing_api_returns_path_reservation_validation_error_for(base_path,
                      body: { error: }.to_json)
       end
 
+      # Stub a request to get a schema by schema name
+      #
+      # @param [String] schema name
+      #
+      # @example
+      #   stub_publishing_api_has_schemas_for_schema_name(
+      #     "email_address",
+      #     { "email_address" =>  {
+      #         "type": "email_address",
+      #         "required": ["email"],
+      #         "properties": {
+      #           "email": { "type" => "string" },
+      #         },
+      #       },
+      #     }
+      #   )
+      def stub_publishing_api_has_schemas_for_schema_name(schema_name, schema)
+        url = "#{PUBLISHING_API_V2_ENDPOINT}/schemas/#{schema_name}"
+        stub_request(:get, url).to_return(status: 200, body: schema.to_json, headers: {})
+      end
+
+      def stub_publishing_api_schema_name_path_to_return_not_found(schema_name)
+        url = "#{PUBLISHING_API_V2_ENDPOINT}/schemas/#{schema_name}"
+        stub_request(:get, url).to_return(status: 404, headers: { "Content-Type" => "application/json; charset=utf-8" })
+      end
+
+      # Stub a request to get all schemas
+      #
+      #
+      # @example
+      #   stub_publishing_api_has_schemas(
+      #     {
+      #         "email_address" =>  {
+      #           "type": "email_address",
+      #           "required": ["email"],
+      #           "properties": {
+      #             "email": { "type" => "string" },
+      #           },
+      #         },
+      #         "tax_bracket" => {
+      #           "type": "tax_bracket",
+      #           "required": ["code"],
+      #           "properties": {
+      #             "code": { "type" => "string" },
+      #           },
+      #         }
+      #     }
+      #   )
+      def stub_publishing_api_has_schemas(schemas)
+        url = "#{PUBLISHING_API_V2_ENDPOINT}/schemas"
+        stub_request(:get, url).to_return(status: 200, body: schemas.to_json, headers: {})
+      end
+
     private
 
       def stub_publishing_api_put(*args)

test/test_helpers/publishing_api_test.rb

@@ -539,6 +539,78 @@
     end
   end
 
+  describe "#stub_publishing_api_has_schemas" do
+    it "returns the given schemas" do
+      schemas = {
+        "email_address" => {
+          "type": "email_address",
+          "required": %w[email],
+          "properties": {
+            "email": { "type" => "string" },
+          },
+        },
+        "tax_bracket" => {
+          "type": "tax_bracket",
+          "required": %w[code],
+          "properties": {
+            "code": { "type" => "string" },
+          },
+        },
+      }
+
+      stub_publishing_api_has_schemas(
+        schemas,
+      )
+
+      api_response = publishing_api.get_schemas
+
+      assert_equal(
+        schemas.to_json,
+        api_response.to_json,
+      )
+    end
+  end
+
+  describe "#stub_publishing_api_has_schemas_for_schema_name" do
+    it "returns the given schema" do
+      schema_name = "email_address"
+
+      schema = {
+        "email_address" => {
+          "type": "email_address",
+          "required": %w[email],
+          "properties": {
+            "email": { "type" => "string" },
+          },
+        },
+      }
+
+      stub_publishing_api_has_schemas_for_schema_name(
+        schema_name,
+        schema,
+      )
+
+      api_response = publishing_api.get_schema(schema_name)
+
+      assert_equal(
+        schema.to_json,
+        api_response.to_json,
+      )
+    end
+  end
+
+  describe "#stub_publishing_api_schema_name_path_to_return_not_found" do
+    it "returns a GdsApi::HTTPNotFound for a call to get a schema by name" do
+      schema_name = "missing_schema"
+
+      stub_publishing_api_schema_name_path_to_return_not_found(schema_name)
+
+      assert_raises GdsApi::HTTPNotFound do
+        publishing_api.get_schema(schema_name)
+      end
+    end
+  end
+
   describe "#request_json_matching predicate" do
     describe "nested required attribute" do
       let(:matcher) { request_json_matching("a" => { "b" => 1 }) }