Add NUTILS_REQUIRES environment variable

This patch adds the NUTILS_REQUIRES environment variable, which instruct the
require methods and requires decorators in testing that any missing item is not
acceptable and should not result in a skipped test. The variables are set in
appropriate places of the test workflow.

.github/workflows/test.yaml

@@ -73,6 +73,7 @@ jobs:
       MKL_NUM_THREADS: 1
       PYTHONHASHSEED: 0
       NUTILS_TENSORIAL: ${{ matrix.tensorial }}
+      NUTILS_TESTING_REQUIRES: "mod:matplotlib mod:meshio mod:PIL"
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -89,7 +90,9 @@ jobs:
           path: dist/
       - name: Install Graphviz
         if: ${{ matrix.os == 'ubuntu-latest' }}
-        run: sudo apt install -y graphviz
+        run: |
+          sudo apt install -y graphviz
+          echo "NUTILS_TESTING_REQUIRES=$NUTILS_TESTING_REQUIRES app:dot" >> $GITHUB_ENV
       - name: Install Nutils and dependencies
         id: install
         env:
@@ -101,11 +104,14 @@ jobs:
           python -um pip install "$_wheel[import-gmsh,export-mpl]"
       - name: Install Scipy
         if: ${{ matrix.matrix-backend == 'scipy' }}
-        run: python -um pip install --upgrade scipy
+        run: |
+          python -um pip install --upgrade scipy
+          echo "NUTILS_TESTING_REQUIRES=$NUTILS_TESTING_REQUIRES mod:scipy" >> $GITHUB_ENV
       - name: Configure MKL
         if: ${{ matrix.matrix-backend == 'mkl' }}
         run: |
           python -um pip install --upgrade --upgrade-strategy eager mkl
+          echo "NUTILS_TESTING_REQUIRES=$NUTILS_TESTING_REQUIRES lib:mkl_rt" >> $GITHUB_ENV
       - name: Test
         env:
           COVERAGE_ID: ${{ matrix.name }}
@@ -203,6 +209,7 @@ jobs:
       # Fixes https://github.com/actions/virtual-environments/issues/3080
       STORAGE_OPTS: overlay.mount_program=/usr/bin/fuse-overlayfs
       _wheel: ${{ needs.build-python-package.outputs.wheel }}
+      NUTILS_TESTING_REQUIRES: "mod:matplotlib mod:meshio mod:PIL lib:mkl_rt"
     steps:
       - name: Checkout
         uses: actions/checkout@v4

nutils/testing.py

@@ -18,6 +18,7 @@
 import logging
 import numpy
 import shutil
+import os
 from nutils import warnings, numeric, _util as util
 
 
@@ -31,6 +32,10 @@ def emit(self, record):
 def _require(category, test, *items):
     missing = [item for item in items if not test(item)]
     if missing:
+        for item in os.getenv(f'NUTILS_TESTING_REQUIRES', '').split():
+            prefix, name = item.split(':')
+            if category.startswith(prefix) and name in missing:
+                raise RuntimeError(f'{category} {required!r} is unexpectedly missing')
         if len(missing) > 1:
             category += 's'
         missing = ', '.join(missing)
@@ -42,6 +47,13 @@ def _test_decorator(test, *args):
         test(*args)
     except unittest.SkipTest as e:
         wrapper = unittest.skip(e)
+    except Exception as outer_exc:
+        inner_exc = outer_exc
+        def wrapper(f):
+            @functools.wraps(f)
+            def wrapped(self):
+                raise inner_exc
+            return wrapped
     else:
         def wrapper(f):
             return f