\def\appleref{apple}
\def\testit#1{%
  \ifnum\pdfstrcmp{#1}{apple}=0
    Yes, it's apple.
  \else
    No, it's #1.
  \fi
}

apple: \testit{apple}

pear: \testit{pear}

\def\fakeapple{apple}

fakeapple: \testit{\fakeapple}

\bye