Unit testing bottle py application that uses request body results in KeyError: 'wsgi.input'

When unit testing a bottle py route function:

from bottle import request, run, post
@post("/blah/<boo>")
def blah(boo):
    body = request.body.readline()
    return "body is %s" % body
blah("booooo!")

The following exception is raised:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in blah
  File "bottle.py", line 1197, in body
    self._body.seek(0)
  File "bottle.py", line 166, in __get__
    if key not in storage: storage[key] = self.getter(obj)
  File "bottle.py", line 1164, in _body
    read_func = self.environ['wsgi.input'].read
KeyError: 'wsgi.input'

The code will work if running as a server via bottle's run function, it's purely when I call it as a normal Python function e.g. in a unit test.

What am I missing? How can I invoke this as a normal python func inside a unit test?