Add test cases to gtid_test.go

[shunki-fujita]

What

moco/pkg/dbop/gtid.go

Lines 24 to 34 in 1338c63

	// There are cases where Retrieved_Gtid_Set is empty,
	// such as when there is no transaction immediately after a fail-over.
	// Therefore, Retrieved_Gtid_Set and Executed_Gtid_Set are unioned to find for the top runner.
	// The union of two GTID sets is simply their joined together with an interposed comma.
	// https://dev.mysql.com/doc/refman/8.0/en/gtid-functions.html
	var gtids string
	if len(repl.RetrievedGtidSet) == 0 {
	gtids = repl.ExecutedGtidSet
	} else {
	gtids = fmt.Sprintf("%s,%s", repl.RetrievedGtidSet, repl.ExecutedGtidSet)
	}

No test exists when RetrievedGtidSet is empty.

How

Describe how to address the issue.

Checklist

• Finish implementation of the issue
• Test all functions
• Have enough logs to trace activities
• Notify developers of necessary actions