feat: allow setting limit in pg_stat_statements (#1205)

Add `.limit` CLI flag to `stat_statements` collector to allow
setting a custom number of queries to be returned.

Signed-off-by: Cristian Greco <cristian@regolo.cc>

collector/pg_stat_statements.go

@@ -24,11 +24,15 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 )
 
-const statStatementsSubsystem = "stat_statements"
+const (
+	statStatementsSubsystem = "stat_statements"
+	defaultStatementLimit   = "100"
+)
 
 var (
 	includeQueryFlag    *bool = nil
 	statementLengthFlag *uint = nil
+	statementLimitFlag  *uint = nil
 )
 
 func init() {
@@ -47,12 +51,18 @@ func init() {
 		"Maximum length of the statement text.").
 		Default("120").
 		Uint()
+	statementLimitFlag = kingpin.Flag(
+		fmt.Sprint(collectorFlagPrefix, statStatementsSubsystem, ".limit"),
+		"Maximum number of statements to return.").
+		Default(defaultStatementLimit).
+		Uint()
 }
 
 type PGStatStatementsCollector struct {
 	log                   *slog.Logger
 	includeQueryStatement bool
 	statementLength       uint
+	statementLimit        uint
 }
 
 func NewPGStatStatementsCollector(config collectorConfig) (Collector, error) {
@@ -60,6 +70,7 @@ func NewPGStatStatementsCollector(config collectorConfig) (Collector, error) {
 		log:                   config.logger,
 		includeQueryStatement: *includeQueryFlag,
 		statementLength:       *statementLengthFlag,
+		statementLimit:        *statementLimitFlag,
 	}, nil
 }
 
@@ -126,9 +137,9 @@ const (
 			FROM pg_stat_statements
 		)
 	ORDER BY seconds_total DESC
-	LIMIT 100;`
+	LIMIT %s;`
 
-	pgStatStatementsNewQuery = `SELECT
+	pgStatStatementsQuery_PG13 = `SELECT
 		pg_get_userbyid(userid) as user,
 		pg_database.datname,
 		pg_stat_statements.queryid,
@@ -148,7 +159,7 @@ const (
 			FROM pg_stat_statements
 		)
 	ORDER BY seconds_total DESC
-	LIMIT 100;`
+	LIMIT %s;`
 
 	pgStatStatementsQuery_PG17 = `SELECT
 		pg_get_userbyid(userid) as user,
@@ -170,7 +181,7 @@ const (
 			FROM pg_stat_statements
 		)
 	ORDER BY seconds_total DESC
-	LIMIT 100;`
+	LIMIT %s;`
 )
 
 func (c PGStatStatementsCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
@@ -179,20 +190,24 @@ func (c PGStatStatementsCollector) Update(ctx context.Context, instance *instanc
 	case instance.version.GE(semver.MustParse("17.0.0")):
 		queryTemplate = pgStatStatementsQuery_PG17
 	case instance.version.GE(semver.MustParse("13.0.0")):
-		queryTemplate = pgStatStatementsNewQuery
+		queryTemplate = pgStatStatementsQuery_PG13
 	default:
 		queryTemplate = pgStatStatementsQuery
 	}
-	var querySelect = ""
+	querySelect := ""
 	if c.includeQueryStatement {
 		querySelect = fmt.Sprintf(pgStatStatementQuerySelect, c.statementLength)
 	}
-	query := fmt.Sprintf(queryTemplate, querySelect)
+	statementLimit := defaultStatementLimit
+	if c.statementLimit > 0 {
+		statementLimit = fmt.Sprintf("%d", c.statementLimit)
+	}
+	query := fmt.Sprintf(queryTemplate, querySelect, statementLimit)
 
 	db := instance.getDB()
 	rows, err := db.QueryContext(ctx, query)
 
-	var presentQueryIds = make(map[string]struct{})
+	presentQueryIds := make(map[string]struct{})
 
 	if err != nil {
 		return err

collector/pg_stat_statements_test.go

@@ -24,7 +24,7 @@ import (
 	"github.com/smartystreets/goconvey/convey"
 )
 
-func TestPGStateStatementsCollector(t *testing.T) {
+func TestPGStatStatementsCollector(t *testing.T) {
 	db, mock, err := sqlmock.New()
 	if err != nil {
 		t.Fatalf("Error opening a stub db connection: %s", err)
@@ -36,7 +36,7 @@ func TestPGStateStatementsCollector(t *testing.T) {
 	columns := []string{"user", "datname", "queryid", "calls_total", "seconds_total", "rows_total", "block_read_seconds_total", "block_write_seconds_total"}
 	rows := sqlmock.NewRows(columns).
 		AddRow("postgres", "postgres", 1500, 5, 0.4, 100, 0.1, 0.2)
-	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery, ""))).WillReturnRows(rows)
+	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery, "", defaultStatementLimit))).WillReturnRows(rows)
 
 	ch := make(chan prometheus.Metric)
 	go func() {
@@ -67,7 +67,7 @@ func TestPGStateStatementsCollector(t *testing.T) {
 	}
 }
 
-func TestPGStateStatementsCollectorWithStatement(t *testing.T) {
+func TestPGStatStatementsCollectorWithStatement(t *testing.T) {
 	db, mock, err := sqlmock.New()
 	if err != nil {
 		t.Fatalf("Error opening a stub db connection: %s", err)
@@ -79,7 +79,7 @@ func TestPGStateStatementsCollectorWithStatement(t *testing.T) {
 	columns := []string{"user", "datname", "queryid", "LEFT(pg_stat_statements.query, 100) as query", "calls_total", "seconds_total", "rows_total", "block_read_seconds_total", "block_write_seconds_total"}
 	rows := sqlmock.NewRows(columns).
 		AddRow("postgres", "postgres", 1500, "select 1 from foo", 5, 0.4, 100, 0.1, 0.2)
-	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery, fmt.Sprintf(pgStatStatementQuerySelect, 100)))).WillReturnRows(rows)
+	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery, fmt.Sprintf(pgStatStatementQuerySelect, 100), defaultStatementLimit))).WillReturnRows(rows)
 
 	ch := make(chan prometheus.Metric)
 	go func() {
@@ -111,7 +111,51 @@ func TestPGStateStatementsCollectorWithStatement(t *testing.T) {
 	}
 }
 
-func TestPGStateStatementsCollectorNull(t *testing.T) {
+func TestPGStatStatementsCollectorWithStatementAndLimit(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("Error opening a stub db connection: %s", err)
+	}
+	defer db.Close()
+
+	inst := &instance{db: db, version: semver.MustParse("12.0.0")}
+
+	columns := []string{"user", "datname", "queryid", "LEFT(pg_stat_statements.query, 100) as query", "calls_total", "seconds_total", "rows_total", "block_read_seconds_total", "block_write_seconds_total"}
+	rows := sqlmock.NewRows(columns).
+		AddRow("postgres", "postgres", 1500, "select 1 from foo", 5, 0.4, 100, 0.1, 0.2)
+	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery, fmt.Sprintf(pgStatStatementQuerySelect, 100), "10"))).WillReturnRows(rows)
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := PGStatStatementsCollector{includeQueryStatement: true, statementLength: 100, statementLimit: 10}
+
+		if err := c.Update(context.Background(), inst, ch); err != nil {
+			t.Errorf("Error calling PGStatStatementsCollector.Update: %s", err)
+		}
+	}()
+
+	expected := []MetricResult{
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 5},
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 0.4},
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 100},
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 0.1},
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 0.2},
+		{labels: labelMap{"queryid": "1500", "query": "select 1 from foo"}, metricType: dto.MetricType_COUNTER, value: 1},
+	}
+
+	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)
+	}
+}
+
+func TestPGStatStatementsCollectorNull(t *testing.T) {
 	db, mock, err := sqlmock.New()
 	if err != nil {
 		t.Fatalf("Error opening a stub db connection: %s", err)
@@ -123,7 +167,7 @@ func TestPGStateStatementsCollectorNull(t *testing.T) {
 	columns := []string{"user", "datname", "queryid", "calls_total", "seconds_total", "rows_total", "block_read_seconds_total", "block_write_seconds_total"}
 	rows := sqlmock.NewRows(columns).
 		AddRow(nil, nil, nil, nil, nil, nil, nil, nil)
-	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsNewQuery, ""))).WillReturnRows(rows)
+	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery_PG13, "", defaultStatementLimit))).WillReturnRows(rows)
 
 	ch := make(chan prometheus.Metric)
 	go func() {
@@ -154,7 +198,7 @@ func TestPGStateStatementsCollectorNull(t *testing.T) {
 	}
 }
 
-func TestPGStateStatementsCollectorNullWithStatement(t *testing.T) {
+func TestPGStatStatementsCollectorNullWithStatement(t *testing.T) {
 	db, mock, err := sqlmock.New()
 	if err != nil {
 		t.Fatalf("Error opening a stub db connection: %s", err)
@@ -166,7 +210,7 @@ func TestPGStateStatementsCollectorNullWithStatement(t *testing.T) {
 	columns := []string{"user", "datname", "queryid", "LEFT(pg_stat_statements.query, 200) as query", "calls_total", "seconds_total", "rows_total", "block_read_seconds_total", "block_write_seconds_total"}
 	rows := sqlmock.NewRows(columns).
 		AddRow(nil, nil, nil, nil, nil, nil, nil, nil, nil)
-	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsNewQuery, fmt.Sprintf(pgStatStatementQuerySelect, 200)))).WillReturnRows(rows)
+	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery_PG13, fmt.Sprintf(pgStatStatementQuerySelect, 200), defaultStatementLimit))).WillReturnRows(rows)
 
 	ch := make(chan prometheus.Metric)
 	go func() {
@@ -198,7 +242,51 @@ func TestPGStateStatementsCollectorNullWithStatement(t *testing.T) {
 	}
 }
 
-func TestPGStateStatementsCollectorNewPG(t *testing.T) {
+func TestPGStatStatementsCollectorNullWithStatementAndLimit(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("Error opening a stub db connection: %s", err)
+	}
+	defer db.Close()
+
+	inst := &instance{db: db, version: semver.MustParse("13.3.7")}
+
+	columns := []string{"user", "datname", "queryid", "LEFT(pg_stat_statements.query, 200) as query", "calls_total", "seconds_total", "rows_total", "block_read_seconds_total", "block_write_seconds_total"}
+	rows := sqlmock.NewRows(columns).
+		AddRow(nil, nil, nil, nil, nil, nil, nil, nil, nil)
+	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery_PG13, fmt.Sprintf(pgStatStatementQuerySelect, 200), "10"))).WillReturnRows(rows)
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := PGStatStatementsCollector{includeQueryStatement: true, statementLength: 200, statementLimit: 10}
+
+		if err := c.Update(context.Background(), inst, ch); err != nil {
+			t.Errorf("Error calling PGStatStatementsCollector.Update: %s", err)
+		}
+	}()
+
+	expected := []MetricResult{
+		{labels: labelMap{"user": "unknown", "datname": "unknown", "queryid": "unknown"}, metricType: dto.MetricType_COUNTER, value: 0},
+		{labels: labelMap{"user": "unknown", "datname": "unknown", "queryid": "unknown"}, metricType: dto.MetricType_COUNTER, value: 0},
+		{labels: labelMap{"user": "unknown", "datname": "unknown", "queryid": "unknown"}, metricType: dto.MetricType_COUNTER, value: 0},
+		{labels: labelMap{"user": "unknown", "datname": "unknown", "queryid": "unknown"}, metricType: dto.MetricType_COUNTER, value: 0},
+		{labels: labelMap{"user": "unknown", "datname": "unknown", "queryid": "unknown"}, metricType: dto.MetricType_COUNTER, value: 0},
+		{labels: labelMap{"queryid": "unknown", "query": "unknown"}, metricType: dto.MetricType_COUNTER, value: 1},
+	}
+
+	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)
+	}
+}
+
+func TestPGStatStatementsCollector_PG13(t *testing.T) {
 	db, mock, err := sqlmock.New()
 	if err != nil {
 		t.Fatalf("Error opening a stub db connection: %s", err)
@@ -210,7 +298,7 @@ func TestPGStateStatementsCollectorNewPG(t *testing.T) {
 	columns := []string{"user", "datname", "queryid", "calls_total", "seconds_total", "rows_total", "block_read_seconds_total", "block_write_seconds_total"}
 	rows := sqlmock.NewRows(columns).
 		AddRow("postgres", "postgres", 1500, 5, 0.4, 100, 0.1, 0.2)
-	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsNewQuery, ""))).WillReturnRows(rows)
+	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery_PG13, "", defaultStatementLimit))).WillReturnRows(rows)
 
 	ch := make(chan prometheus.Metric)
 	go func() {
@@ -241,7 +329,7 @@ func TestPGStateStatementsCollectorNewPG(t *testing.T) {
 	}
 }
 
-func TestPGStateStatementsCollectorNewPGWithStatement(t *testing.T) {
+func TestPGStatStatementsCollector_PG13_WithStatement(t *testing.T) {
 	db, mock, err := sqlmock.New()
 	if err != nil {
 		t.Fatalf("Error opening a stub db connection: %s", err)
@@ -253,7 +341,7 @@ func TestPGStateStatementsCollectorNewPGWithStatement(t *testing.T) {
 	columns := []string{"user", "datname", "queryid", "LEFT(pg_stat_statements.query, 300) as query", "calls_total", "seconds_total", "rows_total", "block_read_seconds_total", "block_write_seconds_total"}
 	rows := sqlmock.NewRows(columns).
 		AddRow("postgres", "postgres", 1500, "select 1 from foo", 5, 0.4, 100, 0.1, 0.2)
-	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsNewQuery, fmt.Sprintf(pgStatStatementQuerySelect, 300)))).WillReturnRows(rows)
+	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery_PG13, fmt.Sprintf(pgStatStatementQuerySelect, 300), defaultStatementLimit))).WillReturnRows(rows)
 
 	ch := make(chan prometheus.Metric)
 	go func() {
@@ -285,7 +373,51 @@ func TestPGStateStatementsCollectorNewPGWithStatement(t *testing.T) {
 	}
 }
 
-func TestPGStateStatementsCollector_PG17(t *testing.T) {
+func TestPGStatStatementsCollector_PG13_WithStatementAndLimit(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("Error opening a stub db connection: %s", err)
+	}
+	defer db.Close()
+
+	inst := &instance{db: db, version: semver.MustParse("13.3.7")}
+
+	columns := []string{"user", "datname", "queryid", "LEFT(pg_stat_statements.query, 300) as query", "calls_total", "seconds_total", "rows_total", "block_read_seconds_total", "block_write_seconds_total"}
+	rows := sqlmock.NewRows(columns).
+		AddRow("postgres", "postgres", 1500, "select 1 from foo", 5, 0.4, 100, 0.1, 0.2)
+	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery_PG13, fmt.Sprintf(pgStatStatementQuerySelect, 300), "10"))).WillReturnRows(rows)
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := PGStatStatementsCollector{includeQueryStatement: true, statementLength: 300, statementLimit: 10}
+
+		if err := c.Update(context.Background(), inst, ch); err != nil {
+			t.Errorf("Error calling PGStatStatementsCollector.Update: %s", err)
+		}
+	}()
+
+	expected := []MetricResult{
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 5},
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 0.4},
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 100},
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 0.1},
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 0.2},
+		{labels: labelMap{"queryid": "1500", "query": "select 1 from foo"}, metricType: dto.MetricType_COUNTER, value: 1},
+	}
+
+	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)
+	}
+}
+
+func TestPGStatStatementsCollector_PG17(t *testing.T) {
 	db, mock, err := sqlmock.New()
 	if err != nil {
 		t.Fatalf("Error opening a stub db connection: %s", err)
@@ -297,7 +429,7 @@ func TestPGStateStatementsCollector_PG17(t *testing.T) {
 	columns := []string{"user", "datname", "queryid", "calls_total", "seconds_total", "rows_total", "block_read_seconds_total", "block_write_seconds_total"}
 	rows := sqlmock.NewRows(columns).
 		AddRow("postgres", "postgres", 1500, 5, 0.4, 100, 0.1, 0.2)
-	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery_PG17, ""))).WillReturnRows(rows)
+	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery_PG17, "", defaultStatementLimit))).WillReturnRows(rows)
 
 	ch := make(chan prometheus.Metric)
 	go func() {
@@ -328,7 +460,7 @@ func TestPGStateStatementsCollector_PG17(t *testing.T) {
 	}
 }
 
-func TestPGStateStatementsCollector_PG17_WithStatement(t *testing.T) {
+func TestPGStatStatementsCollector_PG17_WithStatement(t *testing.T) {
 	db, mock, err := sqlmock.New()
 	if err != nil {
 		t.Fatalf("Error opening a stub db connection: %s", err)
@@ -340,7 +472,7 @@ func TestPGStateStatementsCollector_PG17_WithStatement(t *testing.T) {
 	columns := []string{"user", "datname", "queryid", "LEFT(pg_stat_statements.query, 300) as query", "calls_total", "seconds_total", "rows_total", "block_read_seconds_total", "block_write_seconds_total"}
 	rows := sqlmock.NewRows(columns).
 		AddRow("postgres", "postgres", 1500, "select 1 from foo", 5, 0.4, 100, 0.1, 0.2)
-	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery_PG17, fmt.Sprintf(pgStatStatementQuerySelect, 300)))).WillReturnRows(rows)
+	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery_PG17, fmt.Sprintf(pgStatStatementQuerySelect, 300), defaultStatementLimit))).WillReturnRows(rows)
 
 	ch := make(chan prometheus.Metric)
 	go func() {
@@ -371,3 +503,47 @@ func TestPGStateStatementsCollector_PG17_WithStatement(t *testing.T) {
 		t.Errorf("there were unfulfilled exceptions: %s", err)
 	}
 }
+
+func TestPGStatStatementsCollector_PG17_WithStatementAndLimit(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("Error opening a stub db connection: %s", err)
+	}
+	defer db.Close()
+
+	inst := &instance{db: db, version: semver.MustParse("17.0.0")}
+
+	columns := []string{"user", "datname", "queryid", "LEFT(pg_stat_statements.query, 300) as query", "calls_total", "seconds_total", "rows_total", "block_read_seconds_total", "block_write_seconds_total"}
+	rows := sqlmock.NewRows(columns).
+		AddRow("postgres", "postgres", 1500, "select 1 from foo", 5, 0.4, 100, 0.1, 0.2)
+	mock.ExpectQuery(sanitizeQuery(fmt.Sprintf(pgStatStatementsQuery_PG17, fmt.Sprintf(pgStatStatementQuerySelect, 300), "10"))).WillReturnRows(rows)
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := PGStatStatementsCollector{includeQueryStatement: true, statementLength: 300, statementLimit: 10}
+
+		if err := c.Update(context.Background(), inst, ch); err != nil {
+			t.Errorf("Error calling PGStatStatementsCollector.Update: %s", err)
+		}
+	}()
+
+	expected := []MetricResult{
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 5},
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 0.4},
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 100},
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 0.1},
+		{labels: labelMap{"user": "postgres", "datname": "postgres", "queryid": "1500"}, metricType: dto.MetricType_COUNTER, value: 0.2},
+		{labels: labelMap{"queryid": "1500", "query": "select 1 from foo"}, metricType: dto.MetricType_COUNTER, value: 1},
+	}
+
+	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)
+	}
+}