Add test for postmaster

Signed-off-by: Felix Yuan <[email protected]>

Author: Sticksman

collector/pg_postmaster.go

@@ -37,11 +37,11 @@ var pgPostMasterStartTimeSeconds = prometheus.NewDesc(
 	[]string{}, nil,
 )
 
+var pgPostmasterQuery = "SELECT pg_postmaster_start_time from pg_postmaster_start_time();"
+
 func (c *PGPostmasterCollector) Update(ctx context.Context, db *sql.DB, ch chan<- prometheus.Metric) error {
 	row := db.QueryRowContext(ctx,
-		`SELECT
-			pg_postmaster_start_time
-		from pg_postmaster_start_time();`)
+		pgPostmasterQuery)
 
 	var startTimeSeconds float64
 	err := row.Scan(&startTimeSeconds)

collector/pg_postmaster_test.go

@@ -0,0 +1,45 @@
+package collector
+
+import (
+	"context"
+	"testing"
+
+	"github.com/DATA-DOG/go-sqlmock"
+	"github.com/prometheus/client_golang/prometheus"
+	dto "github.com/prometheus/client_model/go"
+	"github.com/smartystreets/goconvey/convey"
+)
+
+func TestPgPostmasterCollector(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("Error opening a stub db connection: %s", err)
+	}
+	defer db.Close()
+
+	mock.ExpectQuery(sanitizeQuery(pgPostmasterQuery)).WillReturnRows(sqlmock.NewRows([]string{"pg_postmaster_start_time"}).
+		AddRow(1685739904))
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := PGPostmasterCollector{}
+
+		if err := c.Update(context.Background(), db, ch); err != nil {
+			t.Errorf("Error calling PGPostmasterCollector.Update: %s", err)
+		}
+	}()
+
+	expected := []MetricResult{
+		{labels: labelMap{}, value: 1685739904, metricType: dto.MetricType_GAUGE},
+	}
+	convey.Convey("Metrics comparison", t, func() {
+		for _, expect := range expected {
+			m := readMetric(<-ch)
+			convey.So(expect, convey.ShouldResemble, m)
+		}
+	})
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("there were unfulfilled exceptions: %s", err)
+	}
+}