error

type Caller interface {
	// Caller returns the associated Caller instance.
	Caller() caller.Caller
}

type Error interface {
	// Error implements error.
	Error() string

	// Is tests to see if the test error matches most recent error in the
	// stack.
	Is(error) bool

	// Unwrap returns the wrapped error, if any, otherwise nil.
	Unwrap() error
}

type Wrapper interface {
	// Unwrap returns the next error in the error stack, if any, otherwise
	// nil.
	Unwrap() error
}