QGIS/python/plugins/processing/tests

Algorithm tests

To test algorithms you can add entries into testdata/algorithm_tests.yaml.

This file is structured with yaml syntax.

A basic test appears under the toplevel key tests and looks like this:

• name: centroid algorithm: qgis:polygoncentroids params:
  • type: vector location: qgs name: polys.shp results:
  • id: OUTPUT_LAYER type: vector location: proc name: polys_centroid.geojson

How To

To add a new test you can follow these steps:

Run the algorithm you want to test in QGIS from the processing toolbox. If the result is a vector layer prefer geojson as output for its support of mixed geometry types and good readability. Redirect output to python/plugins/processing/tests/testdata/expected

When you have run the algorithm, go to "Processing" > "History" and find the algorithm which you have just run. This looks like

processing.runalg("qgis:densifygeometries","/home/mku/dev/cpp/qgis/QGIS/tests/testdata/polys.shp",2,"/home/mku/dev/cpp/qgis/QGIS/python/plugins/processing/tests/testdata/polys_densify.geojson")

Open the file python/plugins/processing/tests/testdata/algorithm_tests.yaml, copy an existing test block and adjust it to your needs based on the information found in the history.

The first string from the command goes to the key algorithm, the subsequent ones to params and the last one(s) to results.

The above translates to

- name: densify
  algorithm: qgis:densifygeometriesgivenaninterval
  params:
    - type: vector
      location: qgs
      name: polys.shp
    - 2 # Interval
  results:
    - id: OUTPUT
      type: vector
      location: proc
      name: expected/polys_densify.geojson

Params and results

Trivial type parameters .......................

Params and results are specified as lists:

params:
  - 2
  - string
  - another param

As in the example above they can be plain variables.

Layer type parameters .....................

To specify layers you will have to specify

• the type

  • vector or raster

• a location to allow using files from the shared qgis test data

  • qgs will look for the file in the src/tests/testdata
  • proc will look for the file in python/plugins/processing/tests/testdata you should use this location for expected data.

• a name

  • relative path like expected/polys_centroid.geojson

  params:

  • 2
  • string
  • type: vector location: qgs name: polys.shp
  • another param

Results .......

Results have a special key id which is required because an algorithm can produce multiple results. If you don't know the id, just start with OUTPUT and run the test. You will be told if it was wrong and about the possible values.

To deal with a certain tolerance for output values you can specify a compare property for an output.

For a vector layer this means

OUTPUT:
  type: vector
  name: expected/abcd.geojson
compare:
  fields:
    __all__:
      precision: 5 # compare to a precision of .00001 on all fields
    A: skip # skip field A
  geometry:
    precision: 5 # compare coordinates with a precision of 5 digits