add support for /schemas end points in Publishing API

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

This adds methods to the publishing_api adapter

[1] alphagov/publishing-api#2767

lib/gds_api/publishing_api.rb

@@ -487,6 +487,53 @@ def destroy_intent(base_path)
     e
   end
 
+  # Get all schemas
+  #
+  # @return [GdsApi::Response] A map of schema names with JSON schemas.
+  #
+  # @example
+  #
+  #   publishing_api.get_schemas()
+  #     # => {
+  #       "email_address" => {
+  #           "type": "email_address",
+  #           "required": ["email"],
+  #           "properties": {
+  #             "email": { "type" => "string" },
+  #           },
+  #         }
+  #     }
+  #
+  # @see https://github.com/alphagov/publishing-api/blob/main/docs/api.md#get-v2schemas
+  def get_schemas
+    get_json("#{endpoint}/v2/schemas").to_hash
+  end
+
+  # Get a content schema by name
+  #
+  # @param schema_name [String]
+  #
+  # @return [GdsApi::Response] A response mapping schema name with JSON schema.
+  #
+  # @example
+  #
+  #   publishing_api.get_schema("email_address")
+  #     # => {
+  #       "email_address" => {
+  #           "type": "email_address",
+  #           "required": ["email"],
+  #           "properties": {
+  #             "email": { "type" => "string" },
+  #           },
+  #         }
+  #     }
+  #
+  # @raise [HTTPNotFound] when the schema is not found
+  # @see https://github.com/alphagov/publishing-api/blob/main/docs/api.md#get-v2schemasschema_name
+  def get_schema(schema_name)
+    get_json("#{endpoint}/v2/schemas/#{schema_name}").to_hash
+  end
+
 private
 
   def content_url(content_id, params = {})

test/pacts/publishing_api/get_schema_by_name_pact_test.rb

@@ -0,0 +1,56 @@
+require "test_helper"
+require "gds_api/publishing_api"
+
+describe "GdsApi::PublishingApi#get_schemas pact tests" do
+  include PactTest
+
+  let(:api_client) { GdsApi::PublishingApi.new(publishing_api_host) }
+
+  let(:schema) do
+    {
+      "email_address": { "some": "schema" },
+    }
+  end
+
+  describe "when a schema is found" do
+    before do
+      publishing_api
+        .given("there is a schema with given name")
+        .upon_receiving("a get schema by name request")
+        .with(
+          method: :get,
+          path: "/v2/schemas/email_address",
+        )
+        .will_respond_with(
+          status: 200,
+          body: :schema,
+        )
+    end
+
+    it "returns the named schema" do
+      response = api_client.get_schemas
+      assert_equal 200, response.code
+      assert_equal :schema, response.body
+    end
+  end
+
+  describe "when a schema is not found" do
+    before do
+      publishing_api
+        .given("there is not a schema for a given name")
+        .upon_receiving("a get schema by name request")
+        .with(
+          method: :get,
+          path: "/v2/schemas/email_address",
+        )
+        .will_respond_with(
+          status: 404,
+        )
+    end
+
+    it "returns a 404 error" do
+      response = api_client.get_schema("email_address")
+      assert_equal 404, response.code
+    end
+  end
+end

test/pacts/publishing_api/get_schemas_pact_test.rb

@@ -0,0 +1,35 @@
+require "test_helper"
+require "gds_api/publishing_api"
+
+describe "GdsApi::PublishingApi##get_schemas_by_name pact tests" do
+  include PactTest
+
+  let(:api_client) { GdsApi::PublishingApi.new(publishing_api_host) }
+
+  let(:schemas) do
+    {
+      "email_address": { "some": "schema" },
+      "tax_licence": { "another": "schema" },
+    }
+  end
+
+  before do
+    publishing_api
+      .given("there are two schemas")
+      .upon_receiving("a get schemas request")
+      .with(
+        method: :get,
+        path: "/v2/schemas",
+      )
+      .will_respond_with(
+        status: 200,
+        body: :schemas,
+      )
+  end
+
+  it "returns all the schemas" do
+    response = api_client.get_schemas
+    assert_equal 200, response.code
+    assert_equal :schemas, response.body
+  end
+end