Fix test for Python 3.7+

A bare string is interpreted as a module docstring and does not trigger
the usual side-effect.

IPython/core/compilerop.py

@@ -90,13 +90,31 b' class CachingCompiler(codeop.Compile):'
         # stdlib that call it outside our control go through our codepath
         # (otherwise we'd lose our tracebacks).
         linecache.checkcache = check_linecache_ipython
+
+
+    def _fix_module_ds(self, module):
+        """
+        Starting in python 3.7 the AST for mule have changed, and if
+        the first expressions encountered is a string it is attached to the 
+        `docstring` attribute of the `Module` ast node.
+
+        This breaks IPython, as if this string is the only expression, IPython
+        will not return it as the result of the current cell.
+        """
+        from ast import Str, Expr, Module, fix_missing_locations
+        docstring = getattr(module, 'docstring', None)
+        if not docstring:
+            return module
+        new_body=[Expr(Str(docstring, lineno=1, col_offset=0), lineno=1, col_offset=0)]
+        new_body.extend(module.body)
+        return fix_missing_locations(Module(new_body))
         
     def ast_parse(self, source, filename='<unknown>', symbol='exec'):
         """Parse code to an AST with the current compiler flags active.
         
         Arguments are exactly the same as ast.parse (in the standard library),
         and are passed to the built-in compile function."""
-        return compile(source, filename, symbol, self.flags | PyCF_ONLY_AST, 1)
+        return self._fix_module_ds(compile(source, filename, symbol, self.flags | PyCF_ONLY_AST, 1))
     
     def reset_compiler_flags(self):
         """Reset compiler flags to default state."""

IPython/core/interactiveshell.py

@@ -2865,7 +2865,6 b' class InteractiveShell(SingletonConfigurable):'
         """
         if not nodelist:
             return
-
         if interactivity == 'last_expr_or_assign':
             if isinstance(nodelist[-1], _assign_nodes):
                 asg = nodelist[-1]
@@ -2895,7 +2894,6 b' class InteractiveShell(SingletonConfigurable):'
             to_run_exec, to_run_interactive = [], nodelist
         else:
             raise ValueError("Interactivity was %r" % interactivity)
-
         try:
             for i, node in enumerate(to_run_exec):
                 mod = ast.Module([node])