Assertions in Go

assert.go

package main

import (
	"errors"
	"fmt"
	"runtime"
)

func Assert(group string, pairs ...any) error {
	if len(pairs)%2 != 0 {
		return errors.New("assertions must be passed as pairs of string and boolean")
	}

	var errs error
	_, file, no, ok := runtime.Caller(1)
	caller := "<unknown>:0"
	if ok {
		caller = fmt.Sprintf("%s:%d", file, no)
	}

	for i := 0; i < len(pairs); i += 2 {
		id, pred := pairs[i].(string), pairs[i+1].(bool)
		if !pred {
			errs = errors.Join(errs, &AssertionError{Invariant: id, Group: group, Caller: caller})
		}
	}

	return errs
}

func MustAssert(group string, pairs ...any) {
	if err := Assert(group, pairs...); err != nil {
		panic(err)
	}
}

type AssertionError struct {
	Invariant string
	Group     string
	Caller    string
}

func (ae *AssertionError) Error() string {
	return fmt.Sprintf("%s: assertion failed: %s: %s", ae.Caller, ae.Group, ae.Invariant)
}

main.go

package main

func doSomething(x int, species string, data []byte) {
	MustAssert(
		"do-something-inputs",
		"non-zero-operand", x != 0,
		"species-is-cat", species == "cat",
		"non-empty-data", len(data) > 0,
	)

	// Do something with arguments
}

func main() {
	doSomething(0, "dog", nil)
}

output.txt

panic: /tmp/sandbox1646294625/assert.go:32: assertion failed: do-something-inputs: non-zero-operand
/tmp/sandbox1646294625/assert.go:32: assertion failed: do-something-inputs: species-is-cat
/tmp/sandbox1646294625/assert.go:32: assertion failed: do-something-inputs: non-empty-data

goroutine 1 [running]:
main.MustAssert(...)
	/tmp/sandbox1646294625/assert.go:33
main.doSomething(0x60?, {0x49ab61?, 0xc000076058?}, {0x0?, 0x522268?, 0xc0000061c0?})
	/tmp/sandbox1646294625/main.go:4 +0x139
main.main()
	/tmp/sandbox1646294625/main.go:15 +0x29

Program exited.