Add test for cannot write hidden file without extension

Author: serazoli

viper_test.go

@@ -1742,6 +1742,23 @@ func TestSafeWriteConfigAsWithExistingFile(t *testing.T) {
 	assert.True(t, ok, "Expected ConfigFileAlreadyExistsError")
 }
 
+func TestWriteHiddenFile(t *testing.T) {
+	v := New()
+	fs := afero.NewMemMapFs()
+	fs.Create("/test/.config")
+	v.SetFs(fs)
+
+	v.SetConfigName(".config")
+	v.SetConfigType("yaml")
+	v.AddConfigPath("/test")
+
+	err := v.ReadInConfig()
+	require.NoError(t, err)
+
+	err = v.WriteConfig()
+	require.NoError(t, err)
+}
+
 var yamlMergeExampleTgt = []byte(`
 hello:
     pop: 37890