github.com/stretchr/testify v1.8.1: assert.ErrorContains

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/stretchr/testify/assert.ErrorContains in pkg:golang/github.com/stretchr/testify@v1.8.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/stretchr/testify@v1.8.1
Demonstrate these symbols/APIs:
  - github.com/stretchr/testify/assert.ErrorContains

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:a4fc827041d431720e2f4fa3aa6d37f786a9dd697a24613e034e5898a6c8d6aa","contract":["assert.ErrorContains returns true and does not record an error when the error contains the expected substring","assert.ErrorContains returns false and records an error when the error does not contain the expected substring","assert.ErrorContains returns false and records an error when the error is nil","assert.ErrorContains returns true and does not record an error when the search substring is empty and the error is non-nil","assert.ErrorContains performs case-sensitive matching and returns false when casing differs"],"goal":"verify github.com/stretchr/testify/assert.ErrorContains in pkg:golang/github.com/stretchr/testify@v1.8.1","kind":"HOW","packages":["pkg:golang/github.com/stretchr/testify@v1.8.1"],"schemaVersion":1,"symbols":["github.com/stretchr/testify/assert.ErrorContains"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","packageManagerVersion":"1.26.6","runtime":"go","runtimeVersion":"1.26.6","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/stretchr/testify@v1.8.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/stretchr/testify@v1.8.1","symbols":["github.com/stretchr/testify/assert.ErrorContains"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/stretchr/testify v1.8.1

require (
	github.com/davecgh/go-spew v1.1.1 // indirect
	github.com/pmezard/go-difflib v1.0.0 // indirect
	gopkg.in/yaml.v3 v3.0.1 // indirect
)

github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

package main

import (
	"errors"
	"fmt"

	"github.com/stretchr/testify/assert"
)

// Reporter implements assert.TestingT to record assertion outcomes.
type Reporter struct {
	errors []string
	failed bool
}

func (r *Reporter) Errorf(format string, args ...interface{}) {
	r.failed = true
	r.errors = append(r.errors, fmt.Sprintf(format, args...))
}

func main() {
	reporter := &Reporter{}

	// Example 1: Verifying that an error contains the expected substring
	err := errors.New("connection failed: timeout after 30s")
	if assert.ErrorContains(reporter, err, "timeout") {
		fmt.Println("Error contains expected substring 'timeout'")
	}

	// Example 2: Verifying formatted error messages with contextual details
	queryErr := fmt.Errorf("query error on table %s: row not found", "users")
	if assert.ErrorContains(reporter, queryErr, "not found") {
		fmt.Println("Error contains expected substring 'not found'")
	}

	if !reporter.failed {
		fmt.Println("All ErrorContains demonstrations completed successfully.")
	}
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/stretchr/testify/assert.ErrorContains in pkg:golang/github.com/stretchr/testify@v1.8.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/stretchr/testify@v1.8.1"
  ],
  "symbols": [
    "github.com/stretchr/testify/assert.ErrorContains"
  ]
}

package main

import (
	"errors"
	"fmt"
	"os"

	"github.com/stretchr/testify/assert"
)

type contractTestingT struct {
	errors []string
	failed bool
}

func (t *contractTestingT) Errorf(format string, args ...interface{}) {
	t.failed = true
	t.errors = append(t.errors, fmt.Sprintf(format, args...))
}

func main() {
	// Assertion 1: assert.ErrorContains returns true and does not record an error when the error contains the expected substring
	{
		t := &contractTestingT{}
		err := errors.New("database error: connection refused on port 5432")
		if !assert.ErrorContains(t, err, "connection refused") || t.failed || len(t.errors) != 0 {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: ErrorContains should return true for matching substring\n")
			os.Exit(1)
		}
	}

	// Assertion 2: assert.ErrorContains returns false and records an error when the error does not contain the expected substring
	{
		t := &contractTestingT{}
		err := errors.New("file not found: config.yaml")
		if assert.ErrorContains(t, err, "permission denied") || !t.failed || len(t.errors) == 0 {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: ErrorContains should return false and record error for non-matching substring\n")
			os.Exit(1)
		}
	}

	// Assertion 3: assert.ErrorContains returns false and records an error when the error is nil
	{
		t := &contractTestingT{}
		var err error = nil
		if assert.ErrorContains(t, err, "expected error") || !t.failed || len(t.errors) == 0 {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: ErrorContains should return false and record error when error is nil\n")
			os.Exit(1)
		}
	}

	// Assertion 4: assert.ErrorContains returns true and does not record an error when the search substring is empty and the error is non-nil
	{
		t := &contractTestingT{}
		err := errors.New("any non-empty error message")
		if !assert.ErrorContains(t, err, "") || t.failed || len(t.errors) != 0 {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: ErrorContains should return true for empty substring with non-nil error\n")
			os.Exit(1)
		}
	}

	// Assertion 5: assert.ErrorContains performs case-sensitive matching and returns false when casing differs
	{
		t := &contractTestingT{}
		err := errors.New("INVALID_ARGUMENT: missing required field")
		if assert.ErrorContains(t, err, "invalid_argument") || !t.failed || len(t.errors) == 0 {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: ErrorContains should fail when substring casing differs\n")
			os.Exit(1)
		}
	}

	fmt.Println("All contract assertions passed successfully.")
}