test: improve reliability of file operations

- Add error handling after writing to a file in `local_file_test.go` test function

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

local_file_test.go

@@ -18,7 +18,10 @@ func TestLocalFile(t *testing.T) {
 		t.Error(err)
 	}
 	defer os.Remove(f.Name())
-	f.WriteString("Gin Web Framework")
+	_, err = f.WriteString("Gin Web Framework")
+	if err != nil {
+		t.Error(err)
+	}
 	f.Close()
 
 	dir, filename := filepath.Split(f.Name())