Add a test for the assert statement

Author: Yury Selivanov

test/expressions/expr8.py

@@ -0,0 +1,11 @@
+assert a or b, 'aaa'
+
+
+
+assert        : keyword.control.flow.python, source.python
+ a            : source.python
+or            : keyword.operator.python, source.python
+ b,           : source.python
+'             : punctuation.definition.string.begin.python, source.python, string.quoted.single.python
+aaa           : source.python, string.quoted.single.python
+'             : punctuation.definition.string.end.python, source.python, string.quoted.single.python