removes duplicated utility function (#652)

Author: chavacava

rule/exported.go

@@ -23,7 +23,7 @@ type ExportedRule struct {
 func (r *ExportedRule) Apply(file *lint.File, args lint.Arguments) []lint.Failure {
 	var failures []lint.Failure
 
-	if isTest(file) {
+	if file.IsTest() {
 		return failures
 	}
 

rule/package-comments.go

@@ -20,7 +20,7 @@ type PackageCommentsRule struct{}
 func (r *PackageCommentsRule) Apply(file *lint.File, _ lint.Arguments) []lint.Failure {
 	var failures []lint.Failure
 
-	if isTest(file) {
+	if file.IsTest() {
 		return failures
 	}
 

rule/utils.go

@@ -19,10 +19,6 @@ const styleGuideBase = "https://golang.org/wiki/CodeReviewComments"
 // If id == nil, the answer is false.
 func isBlank(id *ast.Ident) bool { return id != nil && id.Name == "_" }
 
-func isTest(f *lint.File) bool {
-	return strings.HasSuffix(f.Name, "_test.go")
-}
-
 var commonMethods = map[string]bool{
 	"Error":     true,
 	"Read":      true,