qgis: add nixos tests

Add NixOS test for QGIS and QGIS-LTR. This test creates QGIS vector
memory layer containing Nix snowflake. This proves that application can
successfully start and Python bindings are working.

By default, Python script is executed in non-interactive mode and QGIS
is closed after script is finished. This script can be also executed
interactively by running following command:

```
nix-build -A qgis
QGIS_TEST_INTERACTIVE=True ./result/bin/qgis --code pkgs/applications/gis/qgis/test.py
```

In this case, QGIS is not automatically closed.

nixos/tests/all-tests.nix

···
   qboot = handleTestOn ["x86_64-linux" "i686-linux"] ./qboot.nix {};
   qemu-vm-restrictnetwork = handleTest ./qemu-vm-restrictnetwork.nix {};
   qemu-vm-volatile-root = runTest ./qemu-vm-volatile-root.nix;
-  quorum = handleTest ./quorum.nix {};
-  quake3 = handleTest ./quake3.nix {};
+  qgis = handleTest ./qgis.nix { qgisPackage = pkgs.qgis; };
+  qgis-ltr = handleTest ./qgis.nix { qgisPackage = pkgs.qgis-ltr; };
   qownnotes = handleTest ./qownnotes.nix {};
+  quake3 = handleTest ./quake3.nix {};
+  quorum = handleTest ./quorum.nix {};
   rabbitmq = handleTest ./rabbitmq.nix {};
   radarr = handleTest ./radarr.nix {};
   radicale = handleTest ./radicale.nix {};

nixos/tests/qgis.nix

···
+import ./make-test-python.nix ({ pkgs, lib, qgisPackage, ... }:
+  let
+    testScript = pkgs.writeTextFile {
+      name = "qgis-test.py";
+      text = (builtins.readFile ../../pkgs/applications/gis/qgis/test.py);
+    };
+  in
+  {
+    name = "qgis";
+    meta = {
+      maintainers = with lib; [ teams.geospatial.members ];
+    };
+
+    nodes = {
+      machine = { pkgs, ... }: {
+        virtualisation.diskSize = 2 * 1024;
+
+        imports = [ ./common/x11.nix ];
+        environment.systemPackages = [ qgisPackage ];
+
+      };
+    };
+
+    testScript = ''
+      start_all()
+
+      machine.succeed("${qgisPackage}/bin/qgis --version | grep 'QGIS ${qgisPackage.version}'")
+      machine.succeed("${qgisPackage}/bin/qgis --code ${testScript}")
+    '';
+  })

pkgs/applications/gis/qgis/default.nix

···
 { lib
 , makeWrapper
+, nixosTests
 , symlinkJoin
 
 , extraPythonPackages ? (ps: [ ])
···
       --set PYTHONPATH $program_PYTHONPATH
   '';
 
-  passthru.unwrapped = qgis-unwrapped;
+  passthru = {
+    unwrapped = qgis-unwrapped;
+    tests.qgis = nixosTests.qgis;
+  };
 
   meta = qgis-unwrapped.meta;
 }

pkgs/applications/gis/qgis/ltr.nix

···
 { lib
 , makeWrapper
+, nixosTests
 , symlinkJoin
 
 , extraPythonPackages ? (ps: [ ])
···
       --set PYTHONPATH $program_PYTHONPATH
   '';
 
-  passthru.unwrapped = qgis-ltr-unwrapped;
+  passthru = {
+    unwrapped = qgis-ltr-unwrapped;
+    tests.qgis-ltr = nixosTests.qgis-ltr;
+  };
 
   inherit (qgis-ltr-unwrapped) meta;
 }

pkgs/applications/gis/qgis/test.py

···
+# QGIS test script.
+# This script will create vector memory layer containing Nix snowflake.
+
+# Set QGIS_TEST_INTERACTIVE=True to run this script in interactive mode (and see
+# Nix snowflake).
+
+# Run script as following:
+# QGIS_TEST_INTERACTIVE=True ./result/bin/qgis --code pkgs/applications/gis/qgis/test.py
+
+import os
+
+test_interactive = eval(os.getenv("QGIS_TEST_INTERACTIVE", "False"))
+
+def test(test_interactive=False):
+
+    import osgeo  # just to check if geo python modules are available
+    from qgis.core import QgsVectorLayer, QgsFeature, QgsGeometry, QgsProject
+
+    # Nix snowflake as WKT
+    WKT = """
+     MULTIPOLYGON (
+         ((37.10819200000000251 45.01934500000000128, 41.42360200000000248 45.0228350000000006, 43.98593199999999825 46.39836900000000242, 51.11554000000000286 46.39135900000000134, 52.20562400000000025 46.98079299999999847, 51.13812500000000227 47.55708200000000119, 46.12925599999999804 47.56117799999999818, 48.65136199999999889 48.91279899999999969, 46.46644299999999816 50.06610299999999825, 37.10819200000000251 45.01934500000000128)),
+         ((36.37806400000000195 49.06532800000000094, 34.21064499999999953 50.22733199999999698, 29.10392099999999971 50.23055699999999746, 25.55861099999999908 52.15672200000000203, 23.37426999999999921 52.15597100000000097, 22.30527299999999968 51.57995100000000122, 24.79831000000000074 50.22714599999999763, 19.77820099999999925 50.23147999999999769, 17.66315000000000168 49.06561399999999651, 36.37806400000000195 49.06532800000000094)),
+         ((25.51021400000000128 46.84120599999999968, 23.36222199999999916 45.67570500000000067, 25.90661599999999964 44.29694800000000043, 22.32231799999999922 42.37779100000000199, 23.41657500000000169 41.78910799999999881, 25.55307200000000023 41.78884599999999949, 28.06890399999999985 43.13755299999999693, 30.56690599999999947 41.78159999999999741, 34.86687599999999776 41.79416100000000256, 25.51021400000000128 46.84120599999999968)),
+         ((29.60533099999999962 44.88583400000000267, 31.77274900000000102 43.72382000000000346, 36.87947299999999728 43.7205939999999984, 40.42478299999999791 41.79442999999999842, 42.60912400000000133 41.7951929999999976, 43.67812200000000189 42.37121299999999735, 41.18508400000000336 43.72401599999999888, 46.20519399999999877 43.71968400000000088, 48.32024400000000242 44.885548, 29.60533099999999962 44.88583400000000267)),
+         ((28.88739899999999849 48.92013800000000145, 24.57198899999999853 48.9166450000000026, 22.0096589999999992 47.54111400000000032, 14.88005199999999917 47.54812199999999933, 13.78996700000000075 46.95868999999999716, 14.85746600000000051 46.38240100000000155, 19.86633600000000044 46.37830199999999792, 17.34422899999999856 45.02668100000000351, 19.52914900000000031 43.87337800000000243, 28.88739899999999849 48.92013800000000145)),
+         ((25.52133699999999905 46.84445300000000145, 23.37334500000000048 45.67894900000000291, 25.91773900000000097 44.30019200000000268, 22.33344200000000157 42.38103699999999918, 23.4276990000000005 41.79235400000000311, 25.56419500000000156 41.79209199999999669, 28.08002700000000118 43.14079900000000123, 30.57802999999999827 41.78484600000000171, 34.87800000000000011 41.79740699999999975, 25.52133699999999905 46.84445300000000145)),
+         ((25.52133699999999905 46.84445300000000145, 23.37334500000000048 45.67895099999999786, 25.91773900000000097 44.30019200000000268, 22.33344200000000157 42.38103699999999918, 23.4276990000000005 41.79235400000000311, 25.56419500000000156 41.79209199999999669, 28.08002700000000118 43.14079900000000123, 30.57802999999999827 41.78484600000000171, 34.87800000000000011 41.79740699999999975, 25.52133699999999905 46.84445300000000145)),
+         ((25.51021400000000128 46.84120599999999968, 23.36222199999999916 45.67570500000000067, 25.90661599999999964 44.29694800000000043, 22.32231799999999922 42.37779100000000199, 23.41657500000000169 41.78910799999999881, 25.55307200000000023 41.78884599999999949, 28.06890399999999985 43.13755299999999693, 30.56690599999999947 41.78159999999999741, 34.86687599999999776 41.79416100000000256, 25.51021400000000128 46.84120599999999968)),
+         ((40.49807200000000051 47.09720099999999832, 42.64606299999999806 48.26270199999999733, 40.10166999999999859 49.64145899999999756, 43.685966999999998 51.56061600000000311, 42.59170999999999907 52.14929899999999918, 40.45521399999999801 52.1495609999999985, 37.93938099999999736 50.80085400000000107, 35.44137899999999775 52.15680700000000058, 31.14140899999999945 52.14424700000000001, 40.49807200000000051 47.09720099999999832)),
+     )
+    """
+
+    layer = QgsVectorLayer('Polygon?crs=epsg:3857', 'QGIS-on-Nix', 'memory')
+    provider = layer.dataProvider()
+
+    polygon = QgsFeature()
+    geom = QgsGeometry.fromWkt(WKT)
+    polygon.setGeometry(geom)
+    provider.addFeatures([polygon])
+
+    layer.updateExtents()
+    QgsProject.instance().addMapLayers([layer])
+
+    # Make sure our test layer contains exactly one feature
+    assert layer.featureCount() == 1
+
+    if not test_interactive:
+        QgsProject.instance().removeMapLayer(layer)
+        QgsProject.instance().clear()
+
+try:
+    test(test_interactive=test_interactive)
+
+    if not test_interactive:
+        print("QGIS test script was successfully executed.")
+        os._exit(0)  # iface.actionExit().trigger() doesn't work
+
+except Exception as e:
+    if not test_interactive:
+        print("QGIS test script has failed.")
+        print("Error message: {}".format(e))
+        os._exit(1)
+