python3Packages.snappy: add sage tests

see
https://github.com/3-manifolds/SnapPy/blob/3.3_as_released/.github/workflows/sage_test.yml

pkgs/development/python-modules/snappy/default.nix

@@ -1,16 +1,22 @@
 {
   lib,
   stdenv,
-  fetchpatch,
+  fetchFromGitHub,
   python,
   buildPythonPackage,
-  fetchFromGitHub,
+  fetchpatch,
+
+  # build-time dependencies
   setuptools,
-  cypari,
   cython,
+
+  # non-Python runtime dependencies
+  libGL,
+
+  # Python runtime dependencies
+  cypari,
   fxrays,
   ipython,
-  libGL,
   low-index,
   packaging,
   pickleshare,
@@ -20,9 +26,16 @@
   snappy-15-knots,
   snappy-manifolds,
   spherogram,
+  tkinter-gl,
+
+  # documentation
   sphinxHook,
   sphinx-rtd-theme,
-  tkinter-gl,
+
+  # tests
+  runCommand,
+  sage,
+  writableTmpDirAsHomeHook,
 }:
 
 buildPythonPackage rec {
@@ -58,7 +71,7 @@ buildPythonPackage rec {
   postPatch =
     lib.optionalString stdenv.hostPlatform.isLinux ''
       substituteInPlace setup.py \
-        --replace-fail "/usr/include/GL" "${libGL.dev}/include/GL"
+        --replace-fail "/usr/include/GL" "${lib.getDev libGL}/include/GL"
       substituteInPlace freedesktop/share/applications/snappy.desktop \
         --replace-fail "Exec=/usr/bin/env python3 -m snappy.app" "Exec=SnapPy"
     ''
@@ -117,6 +130,25 @@ buildPythonPackage rec {
     runHook postCheck
   '';
 
+  passthru.tests.sage =
+    let
+      sage' = sage.override {
+        extraPythonPackages = ps: [ ps.snappy ];
+        requireSageTests = false;
+      };
+    in
+    runCommand "snappy-sage-tests"
+      {
+        nativeBuildInputs = [
+          sage'
+          writableTmpDirAsHomeHook
+        ];
+      }
+      ''
+        sage -python -m snappy.test --skip-gui
+        touch $out
+      '';
+
   meta = {
     description = "Studying the topology and geometry of 3-manifolds, with a focus on hyperbolic structures";
     changelog = "https://snappy.computop.org/news.html";