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// Copyright 2018 The Prometheus Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package testutil provides helpers to test code using the prometheus package
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// of client_golang.
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//
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// While writing unit tests to verify correct instrumentation of your code, it's
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// a common mistake to mostly test the instrumentation library instead of your
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// own code. Rather than verifying that a prometheus.Counter's value has changed
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// as expected or that it shows up in the exposition after registration, it is
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// in general more robust and more faithful to the concept of unit tests to use
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// mock implementations of the prometheus.Counter and prometheus.Registerer
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// interfaces that simply assert that the Add or Register methods have been
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// called with the expected arguments. However, this might be overkill in simple
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// scenarios. The ToFloat64 function is provided for simple inspection of a
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// single-value metric, but it has to be used with caution.
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//
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// End-to-end tests to verify all or larger parts of the metrics exposition can
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// be implemented with the CollectAndCompare or GatherAndCompare functions. The
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// most appropriate use is not so much testing instrumentation of your code, but
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// testing custom prometheus.Collector implementations and in particular whole
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// exporters, i.e. programs that retrieve telemetry data from a 3rd party source
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// and convert it into Prometheus metrics.
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package testutil
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import (
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"bytes"
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"fmt"
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"io"
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"github.com/prometheus/common/expfmt"
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dto "github.com/prometheus/client_model/go"
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"github.com/prometheus/client_golang/prometheus"
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"github.com/prometheus/client_golang/prometheus/internal"
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)
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// ToFloat64 collects all Metrics from the provided Collector. It expects that
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// this results in exactly one Metric being collected, which must be a Gauge,
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// Counter, or Untyped. In all other cases, ToFloat64 panics. ToFloat64 returns
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// the value of the collected Metric.
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//
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// The Collector provided is typically a simple instance of Gauge or Counter, or
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// – less commonly – a GaugeVec or CounterVec with exactly one element. But any
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// Collector fulfilling the prerequisites described above will do.
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//
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// Use this function with caution. It is computationally very expensive and thus
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// not suited at all to read values from Metrics in regular code. This is really
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// only for testing purposes, and even for testing, other approaches are often
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// more appropriate (see this package's documentation).
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//
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// A clear anti-pattern would be to use a metric type from the prometheus
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// package to track values that are also needed for something else than the
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// exposition of Prometheus metrics. For example, you would like to track the
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// number of items in a queue because your code should reject queuing further
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// items if a certain limit is reached. It is tempting to track the number of
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// items in a prometheus.Gauge, as it is then easily available as a metric for
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// exposition, too. However, then you would need to call ToFloat64 in your
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// regular code, potentially quite often. The recommended way is to track the
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// number of items conventionally (in the way you would have done it without
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// considering Prometheus metrics) and then expose the number with a
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// prometheus.GaugeFunc.
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func ToFloat64(c prometheus.Collector) float64 {
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var (
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m prometheus.Metric
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mCount int
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mChan = make(chan prometheus.Metric)
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done = make(chan struct{})
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)
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go func() {
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for m = range mChan {
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mCount++
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}
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close(done)
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}()
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c.Collect(mChan)
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close(mChan)
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<-done
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if mCount != 1 {
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panic(fmt.Errorf("collected %d metrics instead of exactly 1", mCount))
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}
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pb := &dto.Metric{}
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m.Write(pb)
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if pb.Gauge != nil {
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return pb.Gauge.GetValue()
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}
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if pb.Counter != nil {
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return pb.Counter.GetValue()
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}
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if pb.Untyped != nil {
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return pb.Untyped.GetValue()
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}
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panic(fmt.Errorf("collected a non-gauge/counter/untyped metric: %s", pb))
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}
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// CollectAndCount collects all Metrics from the provided Collector and returns their number.
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//
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// This can be used to assert the number of metrics collected by a given collector after certain operations.
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//
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// This function is only for testing purposes, and even for testing, other approaches
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// are often more appropriate (see this package's documentation).
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func CollectAndCount(c prometheus.Collector) int {
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var (
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mCount int
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mChan = make(chan prometheus.Metric)
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done = make(chan struct{})
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)
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go func() {
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for range mChan {
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mCount++
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}
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close(done)
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}()
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c.Collect(mChan)
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close(mChan)
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<-done
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return mCount
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}
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// CollectAndCompare registers the provided Collector with a newly created
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// pedantic Registry. It then does the same as GatherAndCompare, gathering the
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// metrics from the pedantic Registry.
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func CollectAndCompare(c prometheus.Collector, expected io.Reader, metricNames ...string) error {
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reg := prometheus.NewPedanticRegistry()
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if err := reg.Register(c); err != nil {
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return fmt.Errorf("registering collector failed: %s", err)
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}
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return GatherAndCompare(reg, expected, metricNames...)
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}
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// GatherAndCompare gathers all metrics from the provided Gatherer and compares
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// it to an expected output read from the provided Reader in the Prometheus text
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// exposition format. If any metricNames are provided, only metrics with those
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// names are compared.
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func GatherAndCompare(g prometheus.Gatherer, expected io.Reader, metricNames ...string) error {
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got, err := g.Gather()
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if err != nil {
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return fmt.Errorf("gathering metrics failed: %s", err)
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}
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if metricNames != nil {
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got = filterMetrics(got, metricNames)
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}
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var tp expfmt.TextParser
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wantRaw, err := tp.TextToMetricFamilies(expected)
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if err != nil {
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return fmt.Errorf("parsing expected metrics failed: %s", err)
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}
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want := internal.NormalizeMetricFamilies(wantRaw)
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return compare(got, want)
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}
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// compare encodes both provided slices of metric families into the text format,
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// compares their string message, and returns an error if they do not match.
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// The error contains the encoded text of both the desired and the actual
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// result.
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func compare(got, want []*dto.MetricFamily) error {
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var gotBuf, wantBuf bytes.Buffer
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enc := expfmt.NewEncoder(&gotBuf, expfmt.FmtText)
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for _, mf := range got {
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if err := enc.Encode(mf); err != nil {
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return fmt.Errorf("encoding gathered metrics failed: %s", err)
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}
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}
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enc = expfmt.NewEncoder(&wantBuf, expfmt.FmtText)
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for _, mf := range want {
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if err := enc.Encode(mf); err != nil {
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return fmt.Errorf("encoding expected metrics failed: %s", err)
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}
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}
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if wantBuf.String() != gotBuf.String() {
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return fmt.Errorf(`
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metric output does not match expectation; want:
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%s
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got:
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%s`, wantBuf.String(), gotBuf.String())
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}
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return nil
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}
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func filterMetrics(metrics []*dto.MetricFamily, names []string) []*dto.MetricFamily {
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var filtered []*dto.MetricFamily
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for _, m := range metrics {
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for _, name := range names {
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if m.GetName() == name {
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filtered = append(filtered, m)
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break
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}
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}
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}
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return filtered
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}
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