add doctest in random_expression

pymath/random_expression.py

@@ -31,6 +31,19 @@ class RdExpression(object):
 
     @classmethod
     def set_form(cls, form):
+        """ Define whether RdExpression create expression with Expression (nice render) or if it only replace inside {} not taking care or render
+
+        >>> form = "{a}*{b}"
+        >>> exp = RdExpression(form)()
+        >>> print(type(exp))
+        <class 'pymath.expression.Expression'>
+        >>> RdExpression.set_form("raw")
+        >>> form = "{a}*{b}"
+        >>> exp = RdExpression(form)()
+        >>> print(type(exp))
+        <class 'str'>
+        """
+
         cls.FORM = form
 
     @classmethod
@@ -194,7 +207,8 @@ if __name__ == '__main__':
     rdExp3 = RdExpression(form, cond)
     desc_rdExp(rdExp3)
 
-
+    import doctest
+    doctest.testmod()