Introduce TestCase.require_module

This patch introduces the require_module method to testing.TestCase, and uses
the new capability to simplify the setUp method of DocTestCase.

nutils/testing.py

@@ -27,21 +27,44 @@ def emit(self, record):
         print(record.msg)
 
 
-def _not_has_module(module):
+def _has_module(module):
     try:
         importlib.import_module(module)
     except ImportError:
-        return True
-    else:
         return False
+    else:
+        return True
 
 
-def requires(*modules):
-    missing = tuple(filter(_not_has_module, modules))
+def _require(category, test, *items):
+    missing = [item for item in items if not test(item)]
     if missing:
-        return unittest.skip('missing module{}: {}'.format('s' if len(missing) > 1 else '', ','.join(missing)))
+        if len(missing) > 1:
+            category += 's'
+        missing = ', '.join(missing)
+        raise unittest.SkipTest(f'missing {category}: {missing}')
+
+
+require_module = functools.partial(_require, 'module', _has_module)
+
+
+def _test_decorator(test, *args):
+    try:
+        test(*args)
+    except Exception as outer_exc:
+        inner_exc = outer_exc
+        def wrapper(f):
+            @functools.wraps(f)
+            def wrapped(self):
+                raise inner_exc
+            return wrapped
     else:
-        return lambda func: func
+        def wrapper(f):
+            return f
+    return wrapper
+
+
+requires = functools.partial(_test_decorator, require_module) # decorator version of require_module
 
 
 class _ParametrizedCollection(type):
@@ -247,6 +270,8 @@ def assertAlmostEqual64(self, actual, desired, *, atol=2e-15, rtol=2e-3, dtype='
         status.extend(s[i:i+80] for i in range(0, len(s), 80))
         self.fail('\n'.join(status))
 
+    require_module = staticmethod(require_module)
+
 
 ContextTestCase = TestCase
 

tests/test_docs.py

@@ -29,9 +29,7 @@ def setUp(self):
             if blank and line[indent:].startswith('.. requires:: '):
                 requires.extend(name.strip() for name in line[indent+13:].split(','))
             blank = not line.strip()
-        missing = tuple(filter(nutils.testing._not_has_module, requires))
-        if missing:
-            self.skipTest('missing module{}: {}'.format('s' if len(missing) > 1 else '', ','.join(missing)))
+        self.require_module(*requires)
 
         if 'matplotlib' in requires:
             import matplotlib.testing