if err != nil {
		t.Errorf("read error: %v", err)
	}
	if n != 0 {
		t.Errorf("wrong count; got %d want 0", n)
	}
}

func TestUnreadByte(t *testing.T) {
	b := new(Buffer)

	// check at EOF
	if err := b.UnreadByte(); err == nil {
		t.Fatal("UnreadByte at EOF: got no error")
	}
	if _, err := b.ReadByte(); err == nil {
		t.Fatal("ReadByte at EOF: got no error")
	}

</p>

<h2 id="Errors">Errors</h2>

<p>
The predeclared type <code>error</code> is defined as
</p>

<pre>
type error interface {
	Error() string
}
</pre>

<p>
It is the conventional interface for representing an error condition,
with the nil value representing no error.
For instance, a function to read data from a file might be defined:

// to stay in the language.
func println(args ...Type)

// The error built-in interface type is the conventional interface for
// representing an error condition, with the nil value representing no error.
type error interface {
	Error() string

</p>

<h2 id="Errors">Errors</h2>

<p>
The predeclared type <code>error</code> is defined as
</p>

<pre>
type error interface {
	Error() string
}
</pre>

<p>
It is the conventional interface for representing an error condition,
with the nil value representing no error.
For instance, a function to read data from a file might be defined:

[TestFS] now returns a structured error that can be unwrapped
(via method `Unwrap() []error`). This allows inspecting errors

pkg net, type DNSError struct, UnwrapErr error #63116

pkg net/http, func ParseCookie(string) ([]*Cookie, error) #66008

	MOVF	$1, X5				// ERROR "unsupported constant load"
	MOVBU	X5, (X6)			// ERROR "unsupported unsigned store"
	MOVHU	X5, (X6)			// ERROR "unsupported unsigned store"
	MOVWU	X5, (X6)			// ERROR "unsupported unsigned store"
	MOVF	F0, F1, F2			// ERROR "illegal MOV instruction"
	MOVD	F0, F1, F2			// ERROR "illegal MOV instruction"
	MOV	X10, X11, X12			// ERROR "illegal MOV instruction"

The [DNSError] type now wraps errors caused by timeouts or cancellation.
For example, `errors.Is(someDNSErr, context.DeadlineExceedeed)`

[`x509usepolicies` setting.](/pkg/crypto/x509/#CreateCertificate).


### Go 1.21

Go 1.21 made it a run-time error to call `panic` with a nil interface value,
controlled by the [`panicnil` setting](/pkg/builtin/#panic).

Go 1.21 made it an error for html/template actions to appear inside of an ECMAScript 6
template literal, controlled by the