This is by no means a detailed post about testing Ansible. The main reason I’m writing this down is because I know I’ll forget by a few months time.
Goal:
- Create an Ansible plugin filter to calculate the distance between two coordinates (haversine)
- Write and test the required unit tests (and integration?) for the code to be accepted into Ansible
- Raise a PR to the main project
Background
I was writing an Ansible playbook to check the local traffic site for accidents. The site returns a list of incidents state wide, which, is great, but I was only interested in a 10km radius. Eg:
.....
with_items: “{{ traffic.json.features }}”
when: item | distance(myLong,myLat, item.geometry.coordinates.1, item.geometry.coordinates.0)|int < 10
This looped over a variable with_items and then passed some coordinates through the a custom plugin filter called distance. (Note: Distance was a custom plugin filter which I stored in the plugin_filters directory. I figured I’d go a little further and try to submit to Ansible core.)
Fork
- I’ve forked ansible/ansible from github into my own repo.
- I’ve cloned the repo to my development machine
- Changed directory into the freshly cloned ansible directory and ran `source ./hacking/env-setup`.
Finding where to add the filter code
Haversine (wikipedia) is a maths formula, so, it’s probably best to hang out with other Ansible filters such as power, logarithm, min, max and friends.
Grepping through the source for above brought up this:
./lib/ansible/plugins/filter/mathstuff.py
Perfect! Hopefully.
The code…
Added a function to this file:
def haversine(measurement, lat1, lon1, lat2, lon2):
from math import radians, sin, cos, sqrt, asin
diameter = {
‘m’: 7917.5,
‘km’: 12742}
try:
dlat = radians(float(lat2) – float(lat1))
dlon = radians(float(lon2) – float(lon1))
lat1 = radians(float(lat1))
lat2 = radians(float(lat2))
a = sin(dlat / 2) ** 2 + cos(lat1) * cos(lat2) * sin(dlon / 2) ** 2
c = 2 * asin(sqrt(a))
except (ValueError, TypeError) as e:
raise errors.AnsibleFilterError(‘haversine() only accepts floats: %s’ % str(e))
if measurement in diameter:
return round(diameter[measurement] / 2 * c, 2)
else:
raise errors.AnsibleFilterError(‘haversine() can only be called with km or m’)
Testing
Ansible has a great test setup. I started with the unit tests.
Once again, needed to find out where the math stuff testing hung out. Grep’ing through the test directory found: test/units/plugins/filter/test_mathstuff.py
Copying the format of existing tests I added a few tests:
class TestHaversine:
def test_haversine_non_number(self):
with pytest.raises(AnsibleFilterError, message=’haversine() only accepts floats’):
ms.haversine(‘km’, ‘a’, ‘b’, ‘c’, ‘d’)
with pytest.raises(AnsibleFilterError, message=’haversine() only accepts floats’):
ms.haversine(‘m’, ‘a’, ‘b’, ‘c’, ‘d’)
with pytest.raises(AnsibleFilterError, message=’haversine() can only be called with km or m’):
ms.haversine(‘z’, ‘35.9914928’,’-78.907046′, ‘-33.8523063’, ‘151.2085984’)
def test_km(self):
assert ms.haversine(‘km’, ‘35.9914928’, ‘-78.907046’, ‘-33.8523063’, ‘151.2085984’) == 15490.46
def test_m(self):
assert ms.haversine(‘m’, ‘35.9914928’, ‘-78.907046’, ‘-33.8523063’, ‘151.2085984’) == 9625.31
This was to test:
- That proper
float values were passed through to the function
- That a proper measure was used (km or m)
- That two test calculations calculated and rounded nicely
The quickest way to test after making the change was:
ansible-test units --tox --python 2.7 test/units/plugins/filter/test_mathstuff.py
Other types of testing in Ansible were here.
Test playbook
Of course, better test to ensure it’s actually usable in a playbook:
– hosts: localhost
tasks:
– name: Haversine distance between two lon/lat co-ordinates
debug:
msg: “{{ ‘km’|haversine(‘35.9914928′,’-78.907046′, ‘-33.8523063’, ‘151.2085984’) }}”
– name: Haversine distance between two lon/lat co-ordinates
debug:
msg: “{{ ‘m’|haversine(‘35.9914928′,’-78.907046′, ‘-33.8523063’, ‘151.2085984’) }}”
– name: Haversine distance between two lon/lat co-ordinates
debug:
msg: “{{ ‘m’|haversine(‘a35.9914928′,’-78.907046′, ‘-33.8523063’, ‘151.2085984’) }}”
Which resulted in:
$ ansible-playbook only_filter.yml
PLAY [localhost] *********************************************************************************************************************************************
TASK [Gathering Facts] ***************************************************************************************************************************************
ok: [localhost]
TASK [Haversine distance between two lon/lat co-ordinates] ***************************************************************************************************
ok: [localhost] => {
“msg”: “15490.46”
}
TASK [Haversine distance between two lon/lat co-ordinates] ***************************************************************************************************
ok: [localhost] => {
“msg”: “9625.31”
}
TASK [Haversine distance between two lon/lat co-ordinates] ***************************************************************************************************
fatal: [localhost]: FAILED! => {“msg”: “haversine() only accepts floats: could not convert string to float: a35.9914928”}
to retry, use: –limit @/home/johni/ansible/hacking/ansible/only_filter.retry
PLAY RECAP ***************************************************************************************************************************************************
localhost : ok=3 changed=0 unreachable=0 failed=1