error: Add unwrap (#24)

Add a unwrap func helper

* Unwrap if err is nil then it returns a valid value otherwise it panics

xerror/xerror_test.go

@@ -0,0 +1,24 @@
+package xerror
+
+import (
+	"github.com/duke-git/lancet/internal"
+	"strconv"
+	"testing"
+)
+
+func TestUnwrap(t *testing.T) {
+	assert := internal.NewAssert(t, "TestUnwrap")
+	assert.Equal(42, Unwrap(strconv.Atoi("42")))
+}
+
+func TestUnwrapFail(t *testing.T) {
+	assert := internal.NewAssert(t, "TestUnwrapFail")
+
+	_, err := strconv.Atoi("4o2")
+	defer func() {
+		v := recover()
+		assert.Equal(err.Error(), v.(*strconv.NumError).Error())
+	}()
+
+	Unwrap(strconv.Atoi("4o2"))
+}