Keep underscores when normalizing headers

lib/webmock/util/headers.rb

@@ -9,7 +9,8 @@ class Headers
       def self.normalize_headers(headers)
         return nil unless headers
         array = headers.map { |name, value|
-          [name.to_s.split(/_|-/).map { |segment| segment.capitalize }.join("-"),
+          name = name.to_s.tr("_", "-") if name.is_a? Symbol
+          [name.to_s.split(/(_|-)/).map { |segment| segment.capitalize }.join,
            case value
             when Regexp then value
             when Array then (value.size == 1) ? value.first.to_s : value.map {|v| v.to_s}.sort

spec/unit/request_pattern_spec.rb

@@ -684,9 +684,9 @@ def match(request_signature)
         not_to match(WebMock::RequestSignature.new(:get, "www.example.com", headers: {'Content-Type' => 'image/jpeg'}))
     end
 
-    it "should match even is header keys are declared in different form" do
-      expect(WebMock::RequestPattern.new(:get, "www.example.com", headers: {'ContentLength' => '8888', 'Content-type' => 'image/png'})).
-        to match(WebMock::RequestSignature.new(:get, "www.example.com", headers: {:ContentLength => 8888, 'content_type' => 'image/png'}))
+    it "should match even if header keys are declared in different form" do
+      expect(WebMock::RequestPattern.new(:get, "www.example.com", headers: {'ContentLength' => '8888', 'Content-Type' => 'image/png'})).
+        to match(WebMock::RequestSignature.new(:get, "www.example.com", headers: {:ContentLength => 8888, 'content-type' => 'image/png'}))
     end
 
     it "should match is pattern doesn't have specified headers" do

spec/unit/util/headers_spec.rb

@@ -25,4 +25,20 @@
 
   end
 
+  describe ".normalize_headers" do
+    it "normalizes capitalization for string header names" do
+      expect(described_class.normalize_headers({ "foo-BAR-bAz" => "qUx" }))
+        .to eq({ "Foo-Bar-Baz" => "qUx" })
+    end
+
+    it "stringifies and dasherizes symbol header names" do
+      expect(described_class.normalize_headers({ foo_bar: "qUx" }))
+        .to eq({ "Foo-Bar" => "qUx" })
+    end
+
+    it "respects choice of underscores for string header names" do
+      expect(described_class.normalize_headers({ "foo-BAR_bAz" => "qUx" }))
+        .to eq({ "Foo-Bar_Baz" => "qUx" })
+    end
+  end
 end