worker/server: add basic tests for Pending / Running job metrics

vendor/github.com/prometheus/client_golang/prometheus/testutil/lint.go

@@ -0,0 +1,46 @@
+// Copyright 2020 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package testutil
+
+import (
+	"fmt"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/testutil/promlint"
+)
+
+// CollectAndLint registers the provided Collector with a newly created pedantic
+// Registry. It then calls GatherAndLint with that Registry and with the
+// provided metricNames.
+func CollectAndLint(c prometheus.Collector, metricNames ...string) ([]promlint.Problem, error) {
+	reg := prometheus.NewPedanticRegistry()
+	if err := reg.Register(c); err != nil {
+		return nil, fmt.Errorf("registering collector failed: %w", err)
+	}
+	return GatherAndLint(reg, metricNames...)
+}
+
+// GatherAndLint gathers all metrics from the provided Gatherer and checks them
+// with the linter in the promlint package. If any metricNames are provided,
+// only metrics with those names are checked.
+func GatherAndLint(g prometheus.Gatherer, metricNames ...string) ([]promlint.Problem, error) {
+	got, err := g.Gather()
+	if err != nil {
+		return nil, fmt.Errorf("gathering metrics failed: %w", err)
+	}
+	if metricNames != nil {
+		got = filterMetrics(got, metricNames)
+	}
+	return promlint.NewWithMetricFamilies(got).Lint()
+}

vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint/problem.go

@@ -0,0 +1,33 @@
+// Copyright 2020 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package promlint
+
+import dto "github.com/prometheus/client_model/go"
+
+// A Problem is an issue detected by a linter.
+type Problem struct {
+	// The name of the metric indicated by this Problem.
+	Metric string
+
+	// A description of the issue for this Problem.
+	Text string
+}
+
+// newProblem is helper function to create a Problem.
+func newProblem(mf *dto.MetricFamily, text string) Problem {
+	return Problem{
+		Metric: mf.GetName(),
+		Text:   text,
+	}
+}

vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint/promlint.go

@@ -0,0 +1,123 @@
+// Copyright 2020 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package promlint provides a linter for Prometheus metrics.
+package promlint
+
+import (
+	"errors"
+	"io"
+	"sort"
+
+	dto "github.com/prometheus/client_model/go"
+	"github.com/prometheus/common/expfmt"
+)
+
+// A Linter is a Prometheus metrics linter.  It identifies issues with metric
+// names, types, and metadata, and reports them to the caller.
+type Linter struct {
+	// The linter will read metrics in the Prometheus text format from r and
+	// then lint it, _and_ it will lint the metrics provided directly as
+	// MetricFamily proto messages in mfs. Note, however, that the current
+	// constructor functions New and NewWithMetricFamilies only ever set one
+	// of them.
+	r   io.Reader
+	mfs []*dto.MetricFamily
+
+	customValidations []Validation
+}
+
+// New creates a new Linter that reads an input stream of Prometheus metrics in
+// the Prometheus text exposition format.
+func New(r io.Reader) *Linter {
+	return &Linter{
+		r: r,
+	}
+}
+
+// NewWithMetricFamilies creates a new Linter that reads from a slice of
+// MetricFamily protobuf messages.
+func NewWithMetricFamilies(mfs []*dto.MetricFamily) *Linter {
+	return &Linter{
+		mfs: mfs,
+	}
+}
+
+// AddCustomValidations adds custom validations to the linter.
+func (l *Linter) AddCustomValidations(vs ...Validation) {
+	if l.customValidations == nil {
+		l.customValidations = make([]Validation, 0, len(vs))
+	}
+	l.customValidations = append(l.customValidations, vs...)
+}
+
+// Lint performs a linting pass, returning a slice of Problems indicating any
+// issues found in the metrics stream. The slice is sorted by metric name
+// and issue description.
+func (l *Linter) Lint() ([]Problem, error) {
+	var problems []Problem
+
+	if l.r != nil {
+		d := expfmt.NewDecoder(l.r, expfmt.NewFormat(expfmt.TypeTextPlain))
+
+		mf := &dto.MetricFamily{}
+		for {
+			if err := d.Decode(mf); err != nil {
+				if errors.Is(err, io.EOF) {
+					break
+				}
+
+				return nil, err
+			}
+
+			problems = append(problems, l.lint(mf)...)
+		}
+	}
+	for _, mf := range l.mfs {
+		problems = append(problems, l.lint(mf)...)
+	}
+
+	// Ensure deterministic output.
+	sort.SliceStable(problems, func(i, j int) bool {
+		if problems[i].Metric == problems[j].Metric {
+			return problems[i].Text < problems[j].Text
+		}
+		return problems[i].Metric < problems[j].Metric
+	})
+
+	return problems, nil
+}
+
+// lint is the entry point for linting a single metric.
+func (l *Linter) lint(mf *dto.MetricFamily) []Problem {
+	var problems []Problem
+
+	for _, fn := range defaultValidations {
+		errs := fn(mf)
+		for _, err := range errs {
+			problems = append(problems, newProblem(mf, err.Error()))
+		}
+	}
+
+	if l.customValidations != nil {
+		for _, fn := range l.customValidations {
+			errs := fn(mf)
+			for _, err := range errs {
+				problems = append(problems, newProblem(mf, err.Error()))
+			}
+		}
+	}
+
+	// TODO(mdlayher): lint rules for specific metrics types.
+	return problems
+}

vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint/validation.go

@@ -0,0 +1,34 @@
+// Copyright 2020 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package promlint
+
+import (
+	dto "github.com/prometheus/client_model/go"
+
+	"github.com/prometheus/client_golang/prometheus/testutil/promlint/validations"
+)
+
+type Validation = func(mf *dto.MetricFamily) []error
+
+var defaultValidations = []Validation{
+	validations.LintHelp,
+	validations.LintMetricUnits,
+	validations.LintCounter,
+	validations.LintHistogramSummaryReserved,
+	validations.LintMetricTypeInName,
+	validations.LintReservedChars,
+	validations.LintCamelCase,
+	validations.LintUnitAbbreviations,
+	validations.LintDuplicateMetric,
+}

vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint/validations/counter_validations.go

@@ -0,0 +1,40 @@
+// Copyright 2020 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package validations
+
+import (
+	"errors"
+	"strings"
+
+	dto "github.com/prometheus/client_model/go"
+)
+
+// LintCounter detects issues specific to counters, as well as patterns that should
+// only be used with counters.
+func LintCounter(mf *dto.MetricFamily) []error {
+	var problems []error
+
+	isCounter := mf.GetType() == dto.MetricType_COUNTER
+	isUntyped := mf.GetType() == dto.MetricType_UNTYPED
+	hasTotalSuffix := strings.HasSuffix(mf.GetName(), "_total")
+
+	switch {
+	case isCounter && !hasTotalSuffix:
+		problems = append(problems, errors.New(`counter metrics should have "_total" suffix`))
+	case !isUntyped && !isCounter && hasTotalSuffix:
+		problems = append(problems, errors.New(`non-counter metrics should not have "_total" suffix`))
+	}
+
+	return problems
+}

vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint/validations/duplicate_validations.go

@@ -0,0 +1,37 @@
+// Copyright 2024 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package validations
+
+import (
+	"fmt"
+	"reflect"
+
+	dto "github.com/prometheus/client_model/go"
+)
+
+// LintDuplicateMetric detects duplicate metric.
+func LintDuplicateMetric(mf *dto.MetricFamily) []error {
+	var problems []error
+
+	for i, m := range mf.Metric {
+		for _, k := range mf.Metric[i+1:] {
+			if reflect.DeepEqual(m.Label, k.Label) {
+				problems = append(problems, fmt.Errorf("metric not unique"))
+				break
+			}
+		}
+	}
+
+	return problems
+}

vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint/validations/generic_name_validations.go

@@ -0,0 +1,101 @@
+// Copyright 2020 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package validations
+
+import (
+	"errors"
+	"fmt"
+	"regexp"
+	"strings"
+
+	dto "github.com/prometheus/client_model/go"
+)
+
+var camelCase = regexp.MustCompile(`[a-z][A-Z]`)
+
+// LintMetricUnits detects issues with metric unit names.
+func LintMetricUnits(mf *dto.MetricFamily) []error {
+	var problems []error
+
+	unit, base, ok := metricUnits(*mf.Name)
+	if !ok {
+		// No known units detected.
+		return nil
+	}
+
+	// Unit is already a base unit.
+	if unit == base {
+		return nil
+	}
+
+	problems = append(problems, fmt.Errorf("use base unit %q instead of %q", base, unit))
+
+	return problems
+}
+
+// LintMetricTypeInName detects when the metric type is included in the metric name.
+func LintMetricTypeInName(mf *dto.MetricFamily) []error {
+	if mf.GetType() == dto.MetricType_UNTYPED {
+		return nil
+	}
+
+	var problems []error
+
+	n := strings.ToLower(mf.GetName())
+	typename := strings.ToLower(mf.GetType().String())
+
+	if strings.Contains(n, "_"+typename+"_") || strings.HasSuffix(n, "_"+typename) {
+		problems = append(problems, fmt.Errorf(`metric name should not include type '%s'`, typename))
+	}
+
+	return problems
+}
+
+// LintReservedChars detects colons in metric names.
+func LintReservedChars(mf *dto.MetricFamily) []error {
+	var problems []error
+	if strings.Contains(mf.GetName(), ":") {
+		problems = append(problems, errors.New("metric names should not contain ':'"))
+	}
+	return problems
+}
+
+// LintCamelCase detects metric names and label names written in camelCase.
+func LintCamelCase(mf *dto.MetricFamily) []error {
+	var problems []error
+	if camelCase.FindString(mf.GetName()) != "" {
+		problems = append(problems, errors.New("metric names should be written in 'snake_case' not 'camelCase'"))
+	}
+
+	for _, m := range mf.GetMetric() {
+		for _, l := range m.GetLabel() {
+			if camelCase.FindString(l.GetName()) != "" {
+				problems = append(problems, errors.New("label names should be written in 'snake_case' not 'camelCase'"))
+			}
+		}
+	}
+	return problems
+}
+
+// LintUnitAbbreviations detects abbreviated units in the metric name.
+func LintUnitAbbreviations(mf *dto.MetricFamily) []error {
+	var problems []error
+	n := strings.ToLower(mf.GetName())
+	for _, s := range unitAbbreviations {
+		if strings.Contains(n, "_"+s+"_") || strings.HasSuffix(n, "_"+s) {
+			problems = append(problems, errors.New("metric names should not contain abbreviated units"))
+		}
+	}
+	return problems
+}

vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint/validations/help_validations.go

@@ -0,0 +1,32 @@
+// Copyright 2020 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package validations
+
+import (
+	"errors"
+
+	dto "github.com/prometheus/client_model/go"
+)
+
+// LintHelp detects issues related to the help text for a metric.
+func LintHelp(mf *dto.MetricFamily) []error {
+	var problems []error
+
+	// Expect all metrics to have help text available.
+	if mf.Help == nil {
+		problems = append(problems, errors.New("no help text"))
+	}
+
+	return problems
+}

vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint/validations/histogram_validations.go

@@ -0,0 +1,63 @@
+// Copyright 2020 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package validations
+
+import (
+	"errors"
+	"strings"
+
+	dto "github.com/prometheus/client_model/go"
+)
+
+// LintHistogramSummaryReserved detects when other types of metrics use names or labels
+// reserved for use by histograms and/or summaries.
+func LintHistogramSummaryReserved(mf *dto.MetricFamily) []error {
+	// These rules do not apply to untyped metrics.
+	t := mf.GetType()
+	if t == dto.MetricType_UNTYPED {
+		return nil
+	}
+
+	var problems []error
+
+	isHistogram := t == dto.MetricType_HISTOGRAM
+	isSummary := t == dto.MetricType_SUMMARY
+
+	n := mf.GetName()
+
+	if !isHistogram && strings.HasSuffix(n, "_bucket") {
+		problems = append(problems, errors.New(`non-histogram metrics should not have "_bucket" suffix`))
+	}
+	if !isHistogram && !isSummary && strings.HasSuffix(n, "_count") {
+		problems = append(problems, errors.New(`non-histogram and non-summary metrics should not have "_count" suffix`))
+	}
+	if !isHistogram && !isSummary && strings.HasSuffix(n, "_sum") {
+		problems = append(problems, errors.New(`non-histogram and non-summary metrics should not have "_sum" suffix`))
+	}
+
+	for _, m := range mf.GetMetric() {
+		for _, l := range m.GetLabel() {
+			ln := l.GetName()
+
+			if !isHistogram && ln == "le" {
+				problems = append(problems, errors.New(`non-histogram metrics should not have "le" label`))
+			}
+			if !isSummary && ln == "quantile" {
+				problems = append(problems, errors.New(`non-summary metrics should not have "quantile" label`))
+			}
+		}
+	}
+
+	return problems
+}

vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint/validations/units.go

@@ -0,0 +1,118 @@
+// Copyright 2020 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package validations
+
+import "strings"
+
+// Units and their possible prefixes recognized by this library.  More can be
+// added over time as needed.
+var (
+	// map a unit to the appropriate base unit.
+	units = map[string]string{
+		// Base units.
+		"amperes": "amperes",
+		"bytes":   "bytes",
+		"celsius": "celsius", // Also allow Celsius because it is common in typical Prometheus use cases.
+		"grams":   "grams",
+		"joules":  "joules",
+		"kelvin":  "kelvin", // SI base unit, used in special cases (e.g. color temperature, scientific measurements).
+		"meters":  "meters", // Both American and international spelling permitted.
+		"metres":  "metres",
+		"seconds": "seconds",
+		"volts":   "volts",
+
+		// Non base units.
+		// Time.
+		"minutes": "seconds",
+		"hours":   "seconds",
+		"days":    "seconds",
+		"weeks":   "seconds",
+		// Temperature.
+		"kelvins":    "kelvin",
+		"fahrenheit": "celsius",
+		"rankine":    "celsius",
+		// Length.
+		"inches": "meters",
+		"yards":  "meters",
+		"miles":  "meters",
+		// Bytes.
+		"bits": "bytes",
+		// Energy.
+		"calories": "joules",
+		// Mass.
+		"pounds": "grams",
+		"ounces": "grams",
+	}
+
+	unitPrefixes = []string{
+		"pico",
+		"nano",
+		"micro",
+		"milli",
+		"centi",
+		"deci",
+		"deca",
+		"hecto",
+		"kilo",
+		"kibi",
+		"mega",
+		"mibi",
+		"giga",
+		"gibi",
+		"tera",
+		"tebi",
+		"peta",
+		"pebi",
+	}
+
+	// Common abbreviations that we'd like to discourage.
+	unitAbbreviations = []string{
+		"s",
+		"ms",
+		"us",
+		"ns",
+		"sec",
+		"b",
+		"kb",
+		"mb",
+		"gb",
+		"tb",
+		"pb",
+		"m",
+		"h",
+		"d",
+	}
+)
+
+// metricUnits attempts to detect known unit types used as part of a metric name,
+// e.g. "foo_bytes_total" or "bar_baz_milligrams".
+func metricUnits(m string) (unit, base string, ok bool) {
+	ss := strings.Split(m, "_")
+
+	for _, s := range ss {
+		if base, found := units[s]; found {
+			return s, base, true
+		}
+
+		for _, p := range unitPrefixes {
+			if strings.HasPrefix(s, p) {
+				if base, found := units[s[len(p):]]; found {
+					return s, base, true
+				}
+			}
+		}
+	}
+
+	return "", "", false
+}

vendor/github.com/prometheus/client_golang/prometheus/testutil/testutil.go

@@ -0,0 +1,338 @@
+// Copyright 2018 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package testutil provides helpers to test code using the prometheus package
+// of client_golang.
+//
+// While writing unit tests to verify correct instrumentation of your code, it's
+// a common mistake to mostly test the instrumentation library instead of your
+// own code. Rather than verifying that a prometheus.Counter's value has changed
+// as expected or that it shows up in the exposition after registration, it is
+// in general more robust and more faithful to the concept of unit tests to use
+// mock implementations of the prometheus.Counter and prometheus.Registerer
+// interfaces that simply assert that the Add or Register methods have been
+// called with the expected arguments. However, this might be overkill in simple
+// scenarios. The ToFloat64 function is provided for simple inspection of a
+// single-value metric, but it has to be used with caution.
+//
+// End-to-end tests to verify all or larger parts of the metrics exposition can
+// be implemented with the CollectAndCompare or GatherAndCompare functions. The
+// most appropriate use is not so much testing instrumentation of your code, but
+// testing custom prometheus.Collector implementations and in particular whole
+// exporters, i.e. programs that retrieve telemetry data from a 3rd party source
+// and convert it into Prometheus metrics.
+//
+// In a similar pattern, CollectAndLint and GatherAndLint can be used to detect
+// metrics that have issues with their name, type, or metadata without being
+// necessarily invalid, e.g. a counter with a name missing the “_total” suffix.
+package testutil
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net/http"
+
+	"github.com/kylelemons/godebug/diff"
+	dto "github.com/prometheus/client_model/go"
+	"github.com/prometheus/common/expfmt"
+	"google.golang.org/protobuf/proto"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/internal"
+)
+
+// ToFloat64 collects all Metrics from the provided Collector. It expects that
+// this results in exactly one Metric being collected, which must be a Gauge,
+// Counter, or Untyped. In all other cases, ToFloat64 panics. ToFloat64 returns
+// the value of the collected Metric.
+//
+// The Collector provided is typically a simple instance of Gauge or Counter, or
+// – less commonly – a GaugeVec or CounterVec with exactly one element. But any
+// Collector fulfilling the prerequisites described above will do.
+//
+// Use this function with caution. It is computationally very expensive and thus
+// not suited at all to read values from Metrics in regular code. This is really
+// only for testing purposes, and even for testing, other approaches are often
+// more appropriate (see this package's documentation).
+//
+// A clear anti-pattern would be to use a metric type from the prometheus
+// package to track values that are also needed for something else than the
+// exposition of Prometheus metrics. For example, you would like to track the
+// number of items in a queue because your code should reject queuing further
+// items if a certain limit is reached. It is tempting to track the number of
+// items in a prometheus.Gauge, as it is then easily available as a metric for
+// exposition, too. However, then you would need to call ToFloat64 in your
+// regular code, potentially quite often. The recommended way is to track the
+// number of items conventionally (in the way you would have done it without
+// considering Prometheus metrics) and then expose the number with a
+// prometheus.GaugeFunc.
+func ToFloat64(c prometheus.Collector) float64 {
+	var (
+		m      prometheus.Metric
+		mCount int
+		mChan  = make(chan prometheus.Metric)
+		done   = make(chan struct{})
+	)
+
+	go func() {
+		for m = range mChan {
+			mCount++
+		}
+		close(done)
+	}()
+
+	c.Collect(mChan)
+	close(mChan)
+	<-done
+
+	if mCount != 1 {
+		panic(fmt.Errorf("collected %d metrics instead of exactly 1", mCount))
+	}
+
+	pb := &dto.Metric{}
+	if err := m.Write(pb); err != nil {
+		panic(fmt.Errorf("error happened while collecting metrics: %w", err))
+	}
+	if pb.Gauge != nil {
+		return pb.Gauge.GetValue()
+	}
+	if pb.Counter != nil {
+		return pb.Counter.GetValue()
+	}
+	if pb.Untyped != nil {
+		return pb.Untyped.GetValue()
+	}
+	panic(fmt.Errorf("collected a non-gauge/counter/untyped metric: %s", pb))
+}
+
+// CollectAndCount registers the provided Collector with a newly created
+// pedantic Registry. It then calls GatherAndCount with that Registry and with
+// the provided metricNames. In the unlikely case that the registration or the
+// gathering fails, this function panics. (This is inconsistent with the other
+// CollectAnd… functions in this package and has historical reasons. Changing
+// the function signature would be a breaking change and will therefore only
+// happen with the next major version bump.)
+func CollectAndCount(c prometheus.Collector, metricNames ...string) int {
+	reg := prometheus.NewPedanticRegistry()
+	if err := reg.Register(c); err != nil {
+		panic(fmt.Errorf("registering collector failed: %w", err))
+	}
+	result, err := GatherAndCount(reg, metricNames...)
+	if err != nil {
+		panic(err)
+	}
+	return result
+}
+
+// GatherAndCount gathers all metrics from the provided Gatherer and counts
+// them. It returns the number of metric children in all gathered metric
+// families together. If any metricNames are provided, only metrics with those
+// names are counted.
+func GatherAndCount(g prometheus.Gatherer, metricNames ...string) (int, error) {
+	got, err := g.Gather()
+	if err != nil {
+		return 0, fmt.Errorf("gathering metrics failed: %w", err)
+	}
+	if metricNames != nil {
+		got = filterMetrics(got, metricNames)
+	}
+
+	result := 0
+	for _, mf := range got {
+		result += len(mf.GetMetric())
+	}
+	return result, nil
+}
+
+// ScrapeAndCompare calls a remote exporter's endpoint which is expected to return some metrics in
+// plain text format. Then it compares it with the results that the `expected` would return.
+// If the `metricNames` is not empty it would filter the comparison only to the given metric names.
+func ScrapeAndCompare(url string, expected io.Reader, metricNames ...string) error {
+	resp, err := http.Get(url)
+	if err != nil {
+		return fmt.Errorf("scraping metrics failed: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("the scraping target returned a status code other than 200: %d",
+			resp.StatusCode)
+	}
+
+	scraped, err := convertReaderToMetricFamily(resp.Body)
+	if err != nil {
+		return err
+	}
+
+	wanted, err := convertReaderToMetricFamily(expected)
+	if err != nil {
+		return err
+	}
+
+	return compareMetricFamilies(scraped, wanted, metricNames...)
+}
+
+// CollectAndCompare collects the metrics identified by `metricNames` and compares them in the Prometheus text
+// exposition format to the data read from expected.
+func CollectAndCompare(c prometheus.Collector, expected io.Reader, metricNames ...string) error {
+	reg := prometheus.NewPedanticRegistry()
+	if err := reg.Register(c); err != nil {
+		return fmt.Errorf("registering collector failed: %w", err)
+	}
+	return GatherAndCompare(reg, expected, metricNames...)
+}
+
+// GatherAndCompare gathers all metrics from the provided Gatherer and compares
+// it to an expected output read from the provided Reader in the Prometheus text
+// exposition format. If any metricNames are provided, only metrics with those
+// names are compared.
+func GatherAndCompare(g prometheus.Gatherer, expected io.Reader, metricNames ...string) error {
+	return TransactionalGatherAndCompare(prometheus.ToTransactionalGatherer(g), expected, metricNames...)
+}
+
+// TransactionalGatherAndCompare gathers all metrics from the provided Gatherer and compares
+// it to an expected output read from the provided Reader in the Prometheus text
+// exposition format. If any metricNames are provided, only metrics with those
+// names are compared.
+func TransactionalGatherAndCompare(g prometheus.TransactionalGatherer, expected io.Reader, metricNames ...string) error {
+	got, done, err := g.Gather()
+	defer done()
+	if err != nil {
+		return fmt.Errorf("gathering metrics failed: %w", err)
+	}
+
+	wanted, err := convertReaderToMetricFamily(expected)
+	if err != nil {
+		return err
+	}
+
+	return compareMetricFamilies(got, wanted, metricNames...)
+}
+
+// CollectAndFormat collects the metrics identified by `metricNames` and returns them in the given format.
+func CollectAndFormat(c prometheus.Collector, format expfmt.FormatType, metricNames ...string) ([]byte, error) {
+	reg := prometheus.NewPedanticRegistry()
+	if err := reg.Register(c); err != nil {
+		return nil, fmt.Errorf("registering collector failed: %w", err)
+	}
+
+	gotFiltered, err := reg.Gather()
+	if err != nil {
+		return nil, fmt.Errorf("gathering metrics failed: %w", err)
+	}
+
+	gotFiltered = filterMetrics(gotFiltered, metricNames)
+
+	var gotFormatted bytes.Buffer
+	enc := expfmt.NewEncoder(&gotFormatted, expfmt.NewFormat(format))
+	for _, mf := range gotFiltered {
+		if err := enc.Encode(mf); err != nil {
+			return nil, fmt.Errorf("encoding gathered metrics failed: %w", err)
+		}
+	}
+
+	return gotFormatted.Bytes(), nil
+}
+
+// convertReaderToMetricFamily would read from a io.Reader object and convert it to a slice of
+// dto.MetricFamily.
+func convertReaderToMetricFamily(reader io.Reader) ([]*dto.MetricFamily, error) {
+	var tp expfmt.TextParser
+	notNormalized, err := tp.TextToMetricFamilies(reader)
+	if err != nil {
+		return nil, fmt.Errorf("converting reader to metric families failed: %w", err)
+	}
+
+	// The text protocol handles empty help fields inconsistently. When
+	// encoding, any non-nil value, include the empty string, produces a
+	// "# HELP" line. But when decoding, the help field is only set to a
+	// non-nil value if the "# HELP" line contains a non-empty value.
+	//
+	// Because metrics in a registry always have non-nil help fields, populate
+	// any nil help fields in the parsed metrics with the empty string so that
+	// when we compare text encodings, the results are consistent.
+	for _, metric := range notNormalized {
+		if metric.Help == nil {
+			metric.Help = proto.String("")
+		}
+	}
+
+	return internal.NormalizeMetricFamilies(notNormalized), nil
+}
+
+// compareMetricFamilies would compare 2 slices of metric families, and optionally filters both of
+// them to the `metricNames` provided.
+func compareMetricFamilies(got, expected []*dto.MetricFamily, metricNames ...string) error {
+	if metricNames != nil {
+		got = filterMetrics(got, metricNames)
+		expected = filterMetrics(expected, metricNames)
+		if len(metricNames) > len(got) {
+			var missingMetricNames []string
+			for _, name := range metricNames {
+				if ok := hasMetricByName(got, name); !ok {
+					missingMetricNames = append(missingMetricNames, name)
+				}
+			}
+			return fmt.Errorf("expected metric name(s) not found: %v", missingMetricNames)
+		}
+	}
+
+	return compare(got, expected)
+}
+
+// compare encodes both provided slices of metric families into the text format,
+// compares their string message, and returns an error if they do not match.
+// The error contains the encoded text of both the desired and the actual
+// result.
+func compare(got, want []*dto.MetricFamily) error {
+	var gotBuf, wantBuf bytes.Buffer
+	enc := expfmt.NewEncoder(&gotBuf, expfmt.NewFormat(expfmt.TypeTextPlain))
+	for _, mf := range got {
+		if err := enc.Encode(mf); err != nil {
+			return fmt.Errorf("encoding gathered metrics failed: %w", err)
+		}
+	}
+	enc = expfmt.NewEncoder(&wantBuf, expfmt.NewFormat(expfmt.TypeTextPlain))
+	for _, mf := range want {
+		if err := enc.Encode(mf); err != nil {
+			return fmt.Errorf("encoding expected metrics failed: %w", err)
+		}
+	}
+	if diffErr := diff.Diff(gotBuf.String(), wantBuf.String()); diffErr != "" {
+		return fmt.Errorf(diffErr)
+	}
+	return nil
+}
+
+func filterMetrics(metrics []*dto.MetricFamily, names []string) []*dto.MetricFamily {
+	var filtered []*dto.MetricFamily
+	for _, m := range metrics {
+		for _, name := range names {
+			if m.GetName() == name {
+				filtered = append(filtered, m)
+				break
+			}
+		}
+	}
+	return filtered
+}
+
+func hasMetricByName(metrics []*dto.MetricFamily, name string) bool {
+	for _, mf := range metrics {
+		if mf.GetName() == name {
+			return true
+		}
+	}
+	return false
+}