Relocate binding body tests (#2086)

* Relocate binding body tests

Every test file should be related to a tested file.
Remove useless tests.

* Add github.com/stretchr/testify/require package

binding/xml_test.go

@@ -0,0 +1,25 @@
+// Copyright 2019 Gin Core Team. All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+package binding
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestXMLBindingBindBody(t *testing.T) {
+	var s struct {
+		Foo string `xml:"foo"`
+	}
+	xmlBody := `<?xml version="1.0" encoding="UTF-8"?>
+<root>
+   <foo>FOO</foo>
+</root>`
+	err := xmlBinding{}.BindBody([]byte(xmlBody), &s)
+	require.NoError(t, err)
+	assert.Equal(t, "FOO", s.Foo)
+}