ember-cli: Error when running tests with v2.11

I began seeing the following error in my test output immediately after updating my global CLI to 2.11 (ie before i’d actually updated my project):

global failure (1, 0, 1)
Uncaught SyntaxError: Unexpected token o in JSON at position 1@ 6 ms
Source: 	
http://localhost:7357/1090/tests/index.html?hidepassed:1
Source: at window.onerror (http://localhost:7357/assets/test-support.js:4457:7)

The console contains the following two errors:

VM1874:1 Uncaught SyntaxError: Unexpected token o in JSON at position 1
deserializeMessage	@	testem.js:881
messageListener	@	testem.js:849

and

Failed to parse SourceMap: http://localhost:7357/socket.io/socket.io.js.map

Unfortunately updating the project to 2.11 doesn’t fix the issue. Other than the error appearing when running tests, the app seems to function properly.

Error was confirmed by @liquid-swordsman in the testing slack channel also after upgrade to v2.11

---

Output from ember version --verbose && npm --version:

ember-cli: 2.11.0
http_parser: 2.7.0
node: 6.3.0
v8: 5.0.71.52
uv: 1.9.1
zlib: 1.2.8
ares: 1.10.1-DEV
icu: 57.1
modules: 48
openssl: 1.0.2h
os: linux x64
3.10.3

Tested using Chromium Version 53.0.2785.143