extract func parseFormTag from templatefunc.RenderForm

Extracted a func `parseFormTag` that takes a reflect.StructField
and returns the different positional parts of the `form` structTag
with default values as documented in
http://beego.me/docs/mvc/view/view.md#renderform

This makes RenderForm shorter and makes it possible to test the
parsing separately.

templatefunc_test.go

@@ -15,6 +15,7 @@ import (
 	"net/url"
 	"testing"
 	"time"
+  "reflect"
 )
 
 func TestSubstr(t *testing.T) {
@@ -164,3 +165,41 @@ func TestRenderForm(t *testing.T) {
 		t.Errorf("output should equal `%v` but got `%v`", result, output)
 	}
 }
+
+func TestParseFormTag(t *testing.T) {
+  // create struct to contain field with different types of struct-tag `form`
+	type user struct {
+		All       int `form:"name,text,年龄："`
+		NoName    int `form:",hidden,年龄："`
+    OnlyLabel int `form:",,年龄："`
+    OnlyName  int `form:"name"`
+    Ignored   int `form:"-"`
+  }
+
+	objT := reflect.TypeOf(&user{}).Elem()
+
+  label, name, fType, ignored := parseFormTag(objT.Field(0))
+  if !(name == "name" && label == "年龄：" && fType == "text" && ignored == false) {
+		t.Errorf("Form Tag with name, label and type was not correctly parsed.")
+  }
+
+  label, name, fType, ignored = parseFormTag(objT.Field(1))
+  if !(name == "NoName" && label == "年龄：" && fType == "hidden" && ignored == false) {
+		t.Errorf("Form Tag with label and type but without name was not correctly parsed.")
+  }
+
+  label, name, fType, ignored = parseFormTag(objT.Field(2))
+  if !(name == "OnlyLabel" && label == "年龄：" && fType == "text" && ignored == false) {
+		t.Errorf("Form Tag containing only label was not correctly parsed.")
+  }
+
+  label, name, fType, ignored = parseFormTag(objT.Field(3))
+  if !(name == "name" && label == "OnlyName: " && fType == "text" && ignored == false) {
+    t.Errorf("Form Tag containing only name was not correctly parsed.")
+  }
+
+  label, name, fType, ignored = parseFormTag(objT.Field(4))
+  if (ignored == false) {
+    t.Errorf("Form Tag that should be ignored was not correctly parsed.")
+  }
+}