Fix test suite compatibility with Grape 4.0 (grape=HEAD CI) (#982)

The grape=HEAD canary CI job tracks Grape's development branch to catch
breaking changes before they land in a release. It started failing
because Grape 4.0 changed three internal constructor signatures that
the test helpers rely on:

- Grape::Router::Pattern.new dropped the format: keyword
- Grape::Router::Route.new promoted forward_match from an options-hash
  entry to a required keyword argument
- Grape::Endpoint.new replaced method:/for: with http_methods:/api:

Add a GrapeVersion.satisfy?('>= 4.0.0') branch in
spec/support/route_helper.rb and spec/lib/endpoint_spec.rb to use the
new call shapes against Grape HEAD while leaving existing behavior
untouched for the supported pinned range (2.1–3.x).

Author: numbata

CHANGELOG.md

@@ -8,6 +8,7 @@
 #### Fixes
 
 * [#978](https://github.com/ruby-grape/grape-swagger/pull/978): Fix Grape 3.2+ compatibility: desc kwargs, custom types, multi-type param recovery; bump Grape to `>= 2.1, < 5.0`. See [UPGRADING](UPGRADING.md) - [@numbata](https://github.com/numbata).
+* [#982](https://github.com/ruby-grape/grape-swagger/pull/982): Fix test suite compatibility with Grape 4.0 (grape=HEAD CI) - [@numbata](https://github.com/numbata).
 * Your contribution here.
 
 ### 2.1.4 (2026-02-02)

spec/lib/endpoint_spec.rb

@@ -4,8 +4,12 @@
 
 describe Grape::Endpoint do
   subject do
-    # Grape >= HEAD requires :for (the owner API class) when constructing an Endpoint.
-    described_class.new(Grape::Util::InheritableSetting.new, path: '/', method: :get, for: Class.new(Grape::API))
+    if GrapeVersion.satisfy?('>= 4.0.0')
+      # Grape >= 4.0 requires :http_methods and :api (the owner API class) when constructing an Endpoint.
+      described_class.new(Grape::Util::InheritableSetting.new, path: '/', http_methods: :get, api: Class.new(Grape::API))
+    else
+      described_class.new(Grape::Util::InheritableSetting.new, path: '/', method: :get, for: Class.new(Grape::API))
+    end
   end
 
   describe '.content_types_for' do

spec/support/route_helper.rb

@@ -2,7 +2,17 @@
 
 module RouteHelper
   def self.build(method:, pattern:, options:, origin: nil)
-    if GrapeVersion.satisfy?('>= 3.1.0')
+    if GrapeVersion.satisfy?('>= 4.0.0')
+      pattern_obj = Grape::Router::Pattern.new(
+        origin: origin || pattern,
+        suffix: nil,
+        anchor: options.fetch(:anchor, true),
+        params: options.fetch(:params, {}),
+        version: nil,
+        requirements: options.fetch(:requirements, {})
+      )
+      Grape::Router::Route.new(nil, method, pattern_obj, options, forward_match: options.fetch(:forward_match, false))
+    elsif GrapeVersion.satisfy?('>= 3.1.0')
       pattern_obj = Grape::Router::Pattern.new(
         origin: origin || pattern,
         suffix: nil,