Support :mulitpart env key to env_for to force multipart input

lib/rack/test.rb

@@ -290,6 +290,7 @@ def env_for(uri, env)
 
         params = env.delete(:params)
         query_array = [uri.query]
+        multipart = env.delete(:multipart)
 
         if env['REQUEST_METHOD'] == 'GET'
           # Treat params as query params
@@ -301,7 +302,7 @@ def env_for(uri, env)
           params ||= {}
 
           if params.is_a?(Hash)
-            if data = build_multipart(params)
+            if data = build_multipart(params, false, multipart)
               env[:input] = data
               env['CONTENT_LENGTH'] ||= data.length.to_s
               env['CONTENT_TYPE'] = "#{multipart_content_type(env)}; boundary=#{MULTIPART_BOUNDARY}"

spec/rack/test_spec.rb

@@ -102,6 +102,20 @@
     last_request.POST['foo'].must_equal 'bar'
   end
 
+  it 'supports :multipart when using :params for POST' do
+    request '/', method: :post, params: { 'foo' => 'bar' }
+    last_request.POST['foo'].must_equal 'bar'
+    last_request.env['rack.input'].rewind
+    last_request.env['rack.input'].read.must_equal 'foo=bar'
+  end
+
+  it 'supports :multipart when using :params for POST' do
+    request '/', method: :post, params: { 'foo' => 'bar' }, multipart: true
+    last_request.POST['foo'].must_equal 'bar'
+    last_request.env['rack.input'].rewind
+    last_request.env['rack.input'].read.must_include 'content-disposition: form-data; name="foo"'
+  end
+
   it 'supports sending :query_params for POST' do
     request '/', method: :post, query_params: { 'foo' => 'bar' }
     last_request.GET['foo'].must_equal 'bar'