✅ Generate parser tests from yaml fixtures

Currently defined test types:
* `:parser_assert_equal`: compares parse result to the `expected` data.
* `:parser_pending`: print out yaml which can be inserted into the
  appropriate yaml test fixture file.
* `:assert_parse_failure`: asserts `ResponseParseError` is raised

The two big motivations for this:
1) to simplify generation of test data from RFCs or other sources.
2) to simplify re-use of test data as benchmark data.

Author: nevans

test/net/imap/net_imap_test_helpers.rb

@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+require "net/imap"
+require "test/unit"
+require "yaml"
+
+module NetIMAPTestHelpers
+  module TestFixtureGenerators
+
+    attr_reader :fixtures
+
+    def load_fixture_data(*test_fixture_path)
+      dir = self::TEST_FIXTURE_PATH
+      YAML.unsafe_load_file File.join(dir, *test_fixture_path)
+    end
+
+    def generate_tests_from(fixture_data: nil, fixture_file: nil)
+      fixture_data ||= load_fixture_data fixture_file
+      tests = fixture_data.fetch(:tests)
+
+      tests.each do |name, test|
+        type = test.fetch(:test_type) {
+          test.key?(:expected) ? :parser_assert_equal : :parser_pending
+        }
+        name = "test_#{name}" unless name.start_with? "test_"
+        name = name.to_sym
+        raise "#{name} is already defined" if instance_methods.include?(name)
+        # warn "define_method :#{name} = #{type}..."
+
+        case type
+
+        when :parser_assert_equal
+          test => response:, expected:;
+          define_method name do
+            with_debug do
+              parser = Net::IMAP::ResponseParser.new
+              actual = parser.parse response
+              assert_equal expected, actual
+            end
+          end
+
+        when :parser_pending
+          test => response:;
+          define_method name do
+            with_debug do
+              parser = Net::IMAP::ResponseParser.new
+              actual = parser.parse response
+              puts YAML.dump name => {response:, expected: actual}
+              pend "update tests with expected data..."
+            end
+          end
+
+        when :assert_parse_failure
+          test => response:, message:;
+          define_method name do
+            err = assert_raise(Net::IMAP::ResponseParseError) do
+              Net::IMAP::ResponseParser.new.parse response
+            end
+            assert_match(message, err.message)
+          end
+
+        end
+      end
+
+    end
+  end
+
+  def with_debug(bool = true)
+    Net::IMAP.debug, original = bool, Net::IMAP.debug
+    yield
+  ensure
+    Net::IMAP.debug = original
+  end
+
+end

test/net/imap/test_imap_response_parser.rb

@@ -2,8 +2,14 @@
 
 require "net/imap"
 require "test/unit"
+require_relative "net_imap_test_helpers"
 
 class IMAPResponseParserTest < Test::Unit::TestCase
+  TEST_FIXTURE_PATH = File.join(__dir__, "fixtures/response_parser")
+
+  include NetIMAPTestHelpers
+  extend  NetIMAPTestHelpers::TestFixtureGenerators
+
   def setup
     @do_not_reverse_lookup = Socket.do_not_reverse_lookup
     Socket.do_not_reverse_lookup = true
@@ -13,6 +19,22 @@ def teardown
     Socket.do_not_reverse_lookup = @do_not_reverse_lookup
   end
 
+  ############################################################################
+  # Tests that do no more than parse an example response and assert the result
+  # data has the correct values have been moved to yml test fixtures.
+  #
+  # TODO: add instructions for how to quickly add or update yaml tests
+  ############################################################################
+  # Core IMAP specs, by RFC9051 section (w/ obsolete listed last):
+
+  ############################################################################
+  # IMAP extensions, by RFC:
+
+  ############################################################################
+  # More interesting tests about the behavior, either of the test or of the
+  # response data, should still use normal tests, below
+  ############################################################################
+
   def test_flag_list_many_same_flags
     parser = Net::IMAP::ResponseParser.new
     assert_nothing_raised do