github.com/prometheus/client_model v0.2.0: go.Gauge

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify github.com/prometheus/client_model/go.Gauge in pkg:golang/github.com/prometheus/client_model@v0.2.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/prometheus/client_model@v0.2.0
Demonstrate these symbols/APIs:
  - github.com/prometheus/client_model/go.Gauge

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:8ea2ed637b60ca7365bddef4d144f409dd499fb44e10c15d238d601d49076556","contract":["dto.Gauge.GetValue returns 0 for a nil or uninitialized Gauge, and returns the configured float64 value when set.","dto.Gauge.Reset clears the gauge value so GetValue returns 0.","dto.Gauge implements proto.Message and String returns the protobuf text format representation."],"goal":"verify github.com/prometheus/client_model/go.Gauge in pkg:golang/github.com/prometheus/client_model@v0.2.0","kind":"HOW","packages":["pkg:golang/github.com/prometheus/client_model@v0.2.0"],"schemaVersion":1,"symbols":["github.com/prometheus/client_model/go.Gauge"]},"contractCommand":["go","test","./..."],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","executionContext":"go","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","runtime":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/prometheus/client_model@v0.2.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/prometheus/client_model@v0.2.0","symbols":["github.com/prometheus/client_model/go.Gauge"],"verifierAdapter":"golang@1"}

module example.com/gauge

go 1.26.6

require (
	github.com/golang/protobuf v1.5.4
	github.com/prometheus/client_model v0.2.0
)

require google.golang.org/protobuf v1.33.0 // indirect

github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
github.com/golang/protobuf v1.5.4 h1:i7eJL8qZTpSEXOPTxNKhASYpMn+8e5Q6AdndVa1dWek=
github.com/golang/protobuf v1.5.4/go.mod h1:lnTiLA8Wa4RWRcIUkrtSVa5nRhsEGBg48fD6rSs7xps=
github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
github.com/prometheus/client_model v0.2.0 h1:uq5h0d+GuxiXLJLNABMgp2qUWDPiLvgCzz2dUR+/W/M=
github.com/prometheus/client_model v0.2.0/go.mod h1:xMI15A0UPsDsEKsMN9yxemIoYk6Tm2C1GtYGdfGttqA=
golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
google.golang.org/protobuf v1.33.0 h1:uNO2rsAINq/JlFpSdYEKIZ0uKD/R9cpdv0T+yoGwGmI=
google.golang.org/protobuf v1.33.0/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=

package main

import (
	"fmt"

	"github.com/golang/protobuf/proto"
	dto "github.com/prometheus/client_model/go"
)

func main() {
	gauge := &dto.Gauge{
		Value: proto.Float64(42.5),
	}

	fmt.Printf("Gauge value: %f\n", gauge.GetValue())
	gauge.Reset()
	fmt.Printf("After reset: %f\n", gauge.GetValue())
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/prometheus/client_model/go.Gauge in pkg:golang/github.com/prometheus/client_model@v0.2.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/prometheus/client_model@v0.2.0"
  ],
  "symbols": [
    "github.com/prometheus/client_model/go.Gauge"
  ]
}

package test

import (
	"strings"
	"testing"

	"github.com/golang/protobuf/proto"
	dto "github.com/prometheus/client_model/go"
)

func TestGaugeGetValue(t *testing.T) {
	// Nil gauge returns 0
	var nilGauge *dto.Gauge
	if got := nilGauge.GetValue(); got != 0 {
		t.Errorf("nilGauge.GetValue() = %v, want 0", got)
	}

	// Empty gauge returns 0
	emptyGauge := &dto.Gauge{}
	if got := emptyGauge.GetValue(); got != 0 {
		t.Errorf("emptyGauge.GetValue() = %v, want 0", got)
	}

	// Gauge with configured value
	val := 123.456
	gauge := &dto.Gauge{
		Value: proto.Float64(val),
	}
	if got := gauge.GetValue(); got != val {
		t.Errorf("gauge.GetValue() = %v, want %v", got, val)
	}
}

func TestGaugeReset(t *testing.T) {
	gauge := &dto.Gauge{
		Value: proto.Float64(99.9),
	}
	gauge.Reset()
	if got := gauge.GetValue(); got != 0 {
		t.Errorf("gauge.GetValue() after Reset() = %v, want 0", got)
	}
	if gauge.Value != nil {
		t.Errorf("gauge.Value after Reset() = %v, want nil", gauge.Value)
	}
}

func TestGaugeProtoMessageAndString(t *testing.T) {
	gauge := &dto.Gauge{
		Value: proto.Float64(55.5),
	}

	// Verify it implements proto.Message
	var msg proto.Message = gauge
	if msg == nil {
		t.Fatal("gauge does not implement proto.Message")
	}

	str := gauge.String()
	if !strings.Contains(str, "55.5") {
		t.Errorf("gauge.String() = %q, want containing 55.5", str)
	}
}