latex mathtool text not italic code example

Example 1: latex italic text

\textit{text}

Example 2: bold italic text in latex

\documentclass{article}

\makeatletter
\DeclareRobustCommand\bfseriesitshape{%
  \not@math@alphabet\itshapebfseries\relax
  \fontseries\bfdefault
  \fontshape\itdefault
  \selectfont
}
\makeatother

\DeclareTextFontCommand{\textbfit}{\bfseriesitshape}

\begin{document}

\scshape % now the current font shape is small caps

\textit{\textbf{f}}f

\textbf{\textit{f}}f %% causes LaTeX Font Warning

{\fontseries\bfdefault\textit{f}f}

\textbfit{f}f

\end{document}