Function TestClassifyOmniParseError

backend/plugin/parser/tidb/metrics_test.go:23–66

TestClassifyOmniParseError pins the dispatcher fallback classifier against the actual omni error strings — empirically derived against omni v0.0.0-20260513072939-39c04c4cca0f. The classifier must label each known Tier-4 grammar gap correctly so the tidb_dispatcher_omni_fallback_total{reason} counter

(t *testing.T)

// silently mis-label SEQUENCE rejections as "unknown" and lose the entire
// SEQUENCE telemetry signal. The sql parameter is required, not optional.
func TestClassifyOmniParseError(t *testing.T) {
	cases := []struct {
		name     string
		sql      string
		wantOK   bool   // expect parse to fail
		expected string // counter label
	}{
		{
			name:     "FLASHBACK keyword in error msg AND input",
			sql:      "FLASHBACK TABLE foo TO BEFORE DROP;",
			wantOK:   false,
			expected: "flashback",
		},
		{
			name:     "SEQUENCE keyword ONLY in input (omni err says 'after CREATE')",
			sql:      "CREATE SEQUENCE seq;",
			wantOK:   false,
			expected: "sequence",
		},
		// NOTE: BATCH non-transactional DML is now SUPPORTED by omni (grammar
		// merged in omni #157, consumed via the go.mod bump). It therefore
		// parses successfully and no longer reaches the fallback classifier, so
		// the previous "omni rejects BATCH" cases were removed. The classifier's
		// stale BATCH→batch_dml pattern in metrics.go is dead post-support and is
		// tracked for removal as part of the BATCH-support (B1.2) cleanup.
		{
			name:     "genuine syntax error → unknown (no Tier-4 keyword present)",
			sql:      "SELECT FROM WHERE;",
			wantOK:   false,
			expected: "unknown",
		},
	}

	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			_, err := ParseTiDBOmni(tc.sql)
			require.Error(t, err, "test setup expects this input to be rejected by current omni")
			got := classifyOmniParseError(err, tc.sql)
			require.Equal(t, tc.expected, got,
				"classifier must return the correct label for omni err %q + sql %q",
				err.Error(), tc.sql)
		})
	}
}

// TestClassifyOmniParseError_NilErr pins the contract that a nil error
// returns "unknown" — the classifier is called only on the fallback path