Error in units test

I have recently installed Rosetta by compiling from source code. After that, I moved to testing as described here.

$ cd Rosetta/main/source
$ ./scons.py -j4 mode=debug && ./scons.py -j4 mode=debug cat=test
.
(omitted)
.
scons: done building targets.

The commands above seem fine, but when I tried to run unit tests, I got the following error.

$ python test/run.py --mode=debug -j4
Identifying platform...

Traceback (most recent call last):
  File "test/run.py", line 667, in <module>
    if __name__ == "__main__": main(sys.argv)
  File "test/run.py", line 661, in main
    T.runUnitTests()
  File "test/run.py", line 267, in runUnitTests
    self.getPlatformID()
  File "test/run.py", line 89, in getPlatformID
    pl = subprocess.check_output(cmd_str, shell=True).decode('utf-8', errors="replace")
AttributeError: 'module' object has no attribute 'check_output'

Any idea to solve this?

The version of python used is 2.6.9.

Thanks in advance.