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Algorithm tests

To test algorithms you can add entries into testdata/qgis_algorithm_tests.yaml or testdata/gdal_algorithm_tests.yaml as appropriate.

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
      name: polys.gml
  results:
    OUTPUT_LAYER:
      type: vector
      name: expected/polys_centroid.gml

How To

To add a new test please follow these steps:

  1. Run the algorithm you want to test in QGIS from the processing toolbox. If the result is a vector layer prefer GML as output for its support of mixed geometry types and good readability. Redirect output to python/plugins/processing/tests/testdata/expected. For input layers prefer to use what's already there in the folder testdata. If you need extra data, put it into testdata/custom.

  2. When you have run the algorithm, go to Processing > History and find the algorithm which you have just run. Right click the algorithm and click "Create Test". A new window will open with a text definition.

  3. Open the file python/plugins/processing/tests/testdata/algorithm_tests.yaml, copy the text definition there.

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
      name: polys.gml
    - 2 # Interval
  results:
    OUTPUT:
      type: vector
      name: expected/polys_densify.gml

Params and results

Trivial type parameters

Params and results are specified as lists or dictionaries:

params:
  INTERVAL: 5
  INTERPOLATE: True
  NAME: A processing test

or

params:
  - 2
  - string
  - another param

Layer type parameters

You will often need to specify layers as parameters. To specify a layer you will need to specify:

  • the type
    • vector or raster
  • a name
    • relative path like expected/polys_centroid.gml

This is what it looks like in action:

params:
  PAR: 2
  STR: string
  LAYER:
    type: vector
    name: polys.gml
  OTHER: another param

Results

Results are specified very similar.

Basic vector files

It couldn't be more trivial

    OUTPUT:
      name: expected/qgis_intersection.gml
      type: vector

Vector with tolerance

Sometimes different platforms create slightly different results which are still acceptable. In this case (but only then) you may also use additional properties to define how exactly a layer is compared.

To deal with a certain tolerance for output values you can specify a compare property for an output. The compare property can contain sub-properties for fields. This contains information about how precisely a certain field is compared (precision) or a field can even entirely be skiped. There is a special field name __all__ which will apply a certain tolerance to all fields. There is another property geometry which also accepts a precision which is applied to each vertex.

OUTPUT:
  type: vector
  name: expected/abcd.gml
  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

Raster files

Raster files are compared with a hash checksum. This is calculated when you create a test from the processing history.

OUTPUT:
  type: rasterhash
  hash: f1fedeb6782f9389cf43590d4c85ada9155ab61fef6dc285aaeb54d6

Files

You can compare the content of an ouptut file by an expected result reference file

OUTPUT_HTML_FILE:
  name: expected/basic_statistics_string.html
  type: file

Or you can use one or more regular expressions that will be matched against the file content

OUTPUT:
  name: layer_info.html
  type: regex
  rules:
    - 'Extent: \(-1.000000, -3.000000\) - \(11.000000, 5.000000\)'
    - 'Geometry: Line String'
    - 'Feature Count: 6'