7. Processing Algorithms Testing
7.1. Algorithm tests
Note
The original version of these instructions is available at https://github.com/qgis/QGIS/blob/release-3_40/python/plugins/processing/tests/README.md
QGIS provides several algorithms under the Processing framework. You can extend this list with algorithms of your own and, like any new feature, adding tests is required.
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 top level 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
7.1.1. How To
To add a new test please follow these steps:
Run the algorithm you want to test in QGIS from the processing toolbox. If the result is a vector layer prefer GML, with its XSD, 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 foldertestdata
. If you need extra data, put it intotestdata/custom
.When you have run the algorithm, go to
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.
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
It is also possible to create tests for Processing scripts. Scripts should
be placed in the scripts
subdirectory in the test data directory
python/plugins/processing/tests/testdata/
. The script file name
should match the script algorithm name.
7.1.2. Parameters and results
Trivial type parameters
Parameters 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, ie
vector
orraster
a name, with a 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
File type parameters
If you need an external file for the algorithm test, you need to specify the ‘file’ type and the (relative) path to the file in its ‘name’:
params:
PAR: 2
STR: string
EXTFILE:
type: file
name: custom/grass7/extfile.txt
OTHER: another param
Results
Results are specified very similarly.
Basic vector files
It couldn’t be more trivial
OUTPUT:
name: expected/qgis_intersection.gml
type: vector
Add the expected GML and XSD files in the folder.
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 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 skip``ed. 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 output file to 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'
Directories
You can compare the content of an output directory with an expected result reference directory
OUTPUT_DIR:
name: expected/tiles_xyz/test_1
type: directory
7.1.3. Algorithm Context
There are a few more definitions that can modify the context of the algorithm - these can be specified at the top level of test:
project
- will load a specified QGIS project file before running the algorithm. If not specified, the algorithm will run with an empty projectproject_crs
- overrides the default project CRS - e.g.EPSG:27700
ellipsoid
- overrides the default project ellipsoid used for measurements, e.g.GRS80
7.1.4. Running tests locally
ctest -V -R ProcessingQgisAlgorithmsTest
or one of the following values listed in the CMakelists.txt