'return failing source code.'

def getsource(self, astcache=None):

    from _pytest._code.source import getstatementrange_ast
    source = self.frame.code.fullsource
    if (source is None):
        return None
    key = astnode = None
    if (astcache is not None):
        key = self.frame.code.path
        if (key is not None):
            astnode = astcache.get(key, None)
    start = self.getfirstlinesource()
    try:
        (astnode, _, end) = getstatementrange_ast(self.lineno, source, astnode=astnode)
    except SyntaxError:
        end = (self.lineno + 1)
    else:
        if (key is not None):
            astcache[key] = astnode
    return source[start:end]
