Bring Rack::Mock cookie parsing into SPEC (fixes rack#1629)

`#has_key?` isn't required to be supported by the object in the `headers`
element of the response coming back out of the app.  This replaces that call
with a transmogrification into a `HeaderHash` so we can use an index as
normal.  The odd `hash[] || ""` construction is necessary because
`HeaderHash#fetch` doesn't respect header name case insensitivity.

lib/rack/mock.rb

@@ -231,9 +231,11 @@ def cookie(name)
 
     def parse_cookies_from_header
       cookies = Hash.new
-      if original_headers.has_key? 'Set-Cookie'
-        set_cookie_header = original_headers.fetch('Set-Cookie')
-        set_cookie_header.split("\n").each do |cookie|
+      hashed_headers = Rack::Utils::HeaderHash[original_headers]
+      if hashed_headers.has_key?("Set-Cookie")
+        values = (v = hashed_headers["Set-Cookie"]).respond_to?(:to_ary) ? v.to_ary : v.split("\n")
+
+        values.each do |cookie|
           cookie_name, cookie_filling = cookie.split('=', 2)
           cookie_attributes = identify_cookie_attributes cookie_filling
           parsed_cookie = CGI::Cookie.new(

test/spec_mock.rb

@@ -324,6 +324,21 @@
     res.cookie("i_dont_exist").must_be_nil
   end
 
+  it "parses cookie headers provided as an array" do
+    res = Rack::MockRequest.new(->(env) { [200, [["set-cookie", "array=awesome"]], [""]] }).get("")
+    array_cookie = res.cookie("array")
+    array_cookie.value[0].must_equal "awesome"
+  end
+
+  it "parses multiple set-cookie headers provided as an array" do
+    cookie_headers = [["set-cookie", ["array=awesome", "multiple=times"]]]
+    res = Rack::MockRequest.new(->(env) { [200, cookie_headers, [""]] }).get("")
+    array_cookie = res.cookie("array")
+    array_cookie.value[0].must_equal "awesome"
+    second_cookie = res.cookie("multiple")
+    second_cookie.value[0].must_equal "times"
+  end
+
   it "provide access to the HTTP body" do
     res = Rack::MockRequest.new(app).get("")
     res.body.must_match(/rack/)