func (a Assertion) Error(err error, args ...interface{}) {
	if err == nil {
		a.Helper()
		a.Fatal("An error is expected but got nil. " + fmt.Sprint(args...))
	}
}
Error asserts that err is not nil, but if it is nil, it calls Fatal with:
An error is expected but got nil. {args}
package test
import (
	"fmt"
	"sync"
	"testing"
)
type T struct {
	*testing.T
	observations map[string]*observation
}
type observation struct {
	T
	sync.Mutex
	actual []interface{}
	err    error
	done   bool
}
func Describ(e *testing.T, name string, f func(T)) bool {
	e.Helper()
	return e.Run(name, func(t *testing.T) { f(T{T: t}) })
}
func Contex(t T, description string, f func(T)) bool {
	t.Helper()
	return t.Run(description, func(t *testing.T) { f(T{T: t}) })
}
func I(t T, description string, f func(T)) bool {
	t.Helper()
	return t.Run(description, func(t *testing.T) {
		f(T{T: t, observations: make(map[string]*observation)})
	})
}
func Asser(t T) Assertion {
	return Assertion{t.T}
}
type Assertion struct {
	*testing.T
}
func (a Assertion) Must(condition bool, args ...interface{}) {
	if !condition {
		a.Helper()
		a.Fatal("Must have " + fmt.Sprint(args...))
	}
}
func (a Assertion) Not(condition bool, args ...interface{}) {
	if condition {
		a.Helper()
		a.Fatal("Must not have " + fmt.Sprint(args...))
	}
}
func (a Assertion) True(condition bool, args ...interface{}) {
	if !condition {
		a.Helper()
		a.Fatal("Expected " + fmt.Sprint(args...))
	}
}
func (a Assertion) False(condition bool, args ...interface{}) {
	if condition {
		a.Helper()
		a.Fatal("Unexpected " + fmt.Sprint(args...))
	}
}