update unit testing slides with exceptions resolve issue #41

Tutorials/T05-PyUnit/slides/Unit Testing.tex

@@ -304,6 +304,7 @@ True
 \end{lstlisting}
 \end{frame}
 
+
 \begin{frame}[fragile]
 \frametitle{Redundant code in tests}
 \begin{lstlisting}[language=Python, escapechar=!]
@@ -402,6 +403,47 @@ class TestCircles:
 \end{itemize}
 \end{frame}
 
+
+\begin{frame}[fragile]
+\frametitle{Asserting about exceptions}
+\begin{itemize}
+	\item{It is very important in unit testing to check for edge cases and behaviour in the case of unexpected input.}
+	\item{If a function raises an exception in some cases, you should include those cases in your unit testing as well.}
+	\item{You can do so by using a context manager called pytest.raises.}
+\end{itemize}
+\begin{lstlisting}[language=Python, escapechar=!]
+import pytest
+
+def test_zero_division():
+with pytest.raises(ZeroDivisionError):
+1 / 0
+\end{lstlisting}
+\end{frame}
+
+
+\begin{frame}[fragile]
+\frametitle{Asserting about exceptions}
+\begin{itemize}
+	\item{If an exception is not raised in a pytest.raises block, the test will fail.}
+\end{itemize}
+\begin{lstlisting}[language=Python, escapechar=!]
+import pytest
+
+def test_zero_division():
+	with pytest.raises(ZeroDivisionError):
+		2 / 1
+\end{lstlisting}
+\begin{itemize}
+	\item{If you run this test, it will give the result:}
+\end{itemize}
+
+\begin{figure}[b]
+	{\includegraphics[width=8cm]{exception-not-raised}}
+\end{figure}
+
+
+\end{frame}
+
 \begin{frame}[fragile]
 \frametitle{Pytest plugin for measuring coverage}
 	\begin{itemize}
@@ -433,8 +475,9 @@ class TestCircles:
 \begin{frame}[fragile]
 \frametitle{References}
 \begin{itemize}
-	\item {\url{https://docs.pytest.org/en/latest/xunit_setup.html}}
-	\item {\url{https://en.wikipedia.org/wiki/Code_coverage}}
+	\item{\url{https://docs.pytest.org/en/latest/xunit_setup.html}}
+	\item{\url{https://en.wikipedia.org/wiki/Code_coverage}}
+	\item{\url{http://pytest.readthedocs.io/en/reorganize-docs/new-docs/user/pytest_raises.html}}
 \end{itemize}
 \end{frame}