add test case

Author: brian-mckinney

x-pack/osquerybeat/ext/osquery-extension/pkg/encoding/encoding_test.go

@@ -404,6 +404,14 @@ func Test_formatTimeWithTagFormat(t *testing.T) {
 			want:       "0001-01-01T00:00:00Z",
 			wantErr:    false,
 		},
+		{
+			name:       "Zero unix timestamp with UseNumbersZeroValues flag",
+			fieldValue: reflect.ValueOf(time.Time{}),
+			flag:       EncodingFlagUseNumbersZeroValues,
+			tag:        tagPtr(`format:"unix"`),
+			want:       "0",
+			wantErr:    false,
+		},
 		{
 			name:       "With timezone Asia/Tokyo",
 			fieldValue: reflect.ValueOf(time.Date(2023, 6, 15, 14, 30, 0, 0, time.UTC)),