t.Errorf("%s: buf.Len() == %d, len(s) == %d", testname, buf.Len(), len(s))
	}

	if string(bytes) != s {
		t.Errorf("%s: string(buf.Bytes()) == %q, s == %q", testname, string(bytes), s)
	}
}

// Fill buf through n writes of string fus.
// The initial contents of buf corresponds to the string s;
// the result is the final contents of buf returned as a string.

[<a href="#Go_1.13">Go 1.13</a>].
A single <code>0</code> is considered a decimal zero.
In hexadecimal literals, letters <code>a</code> through <code>f</code>
and <code>A</code> through <code>F</code> represent values 10 through 15.
</p>

<p>
For readability, an underscore character <code>_</code> may appear after
a base prefix or between successive digits; such underscores do not change