Add two specs for choosing platform specific gems

spec/resolver/platform_spec.rb

@@ -28,6 +28,49 @@
     end
   end
 
+  it "takes the latest ruby gem, even if an older platform specific version is available" do
+    @index = build_index do
+      gem "foo", "1.0.0"
+      gem "foo", "1.0.0", "x64-mingw32"
+      gem "foo", "1.1.0"
+    end
+    dep "foo"
+    platforms "x64-mingw32"
+
+    should_resolve_as %w[foo-1.1.0]
+  end
+
+  it "takes the ruby version if the platform version is incompatible" do
+    @index = build_index do
+      gem "bar", "1.0.0"
+      gem "foo", "1.0.0"
+      gem "foo", "1.0.0", "x64-mingw32" do
+        dep "bar", "< 1"
+      end
+    end
+    dep "foo"
+    platforms "x64-mingw32"
+
+    should_resolve_as %w[foo-1.0.0]
+  end
+
+  it "takes the latest ruby gem if the platform specific gem doesn't match the required_ruby_version" do
+    @index = build_index do
+      gem "foo", "1.0.0"
+      gem "foo", "1.0.0", "x64-mingw32"
+      gem "foo", "1.1.0"
+      gem "foo", "1.1.0", "x64-mingw32" do |s|
+        s.required_ruby_version = [">= 2.0", "< 2.4"]
+      end
+      gem "ruby\0", "2.5.1"
+    end
+    dep "foo"
+    dep "ruby\0", "2.5.1"
+    platforms "x64-mingw32"
+
+    should_resolve_as %w[foo-1.1.0]
+  end
+
   describe "with mingw32" do
     before :each do
       @index = build_index do