fix unhandled errors and remove unused parameter (#2061)

* fix unhandled errors

* fix unhandled error in cache package test

* omit variable type

* omit variable type

* rename variable because collide with the imported package name

* handle file error on closing

* fix unhandled in common_linux.go

* fix unhandled errors in helpers_test.go

* fix unhandled errors in listen_test.go

* remove unused parameter in emptyHandler method

listen_test.go

@@ -166,12 +166,18 @@ func captureOutput(f func()) string {
 	go func() {
 		var buf bytes.Buffer
 		wg.Done()
-		io.Copy(&buf, reader)
+		_, err := io.Copy(&buf, reader)
+		if err != nil {
+			panic(err)
+		}
 		out <- buf.String()
 	}()
 	wg.Wait()
 	f()
-	writer.Close()
+	err = writer.Close()
+	if err != nil {
+		panic(err)
+	}
 	return <-out
 }
 
@@ -244,6 +250,6 @@ func Test_App_print_Route_with_group(t *testing.T) {
 	utils.AssertEqual(t, true, strings.Contains(printRoutesMessage, "/v1/test/fiber/*"))
 }
 
-func emptyHandler(c *Ctx) error {
+func emptyHandler(_ *Ctx) error {
 	return nil
 }