gh-40677: src/sage/libs/gap: move a few tests to pytest
    
There are two files, `src/sage/libs/gap/test{,_long}.py` that contain
only tests for `sage.libs.gap`. These are doctests for no other reason
than because we had no other way to run them in the past. This commit
moves them to a new file, `gap_test.py`, that will be run by pytest
rather than the doctest runner.

In the process I've tried to explain what I think the tests are doing.
    
URL: #40677
Reported by: Michael Orlitzky
Reviewer(s): Michael Orlitzky, user202729

Author: Release Manager

conftest.py

@@ -341,3 +341,21 @@ def add_imports(doctest_namespace: dict[str, Any]):
     sage_namespace["__name__"] = "__main__"
 
     doctest_namespace.update(**sage_namespace)
+
+
+@pytest.fixture
+def tmpfile():
+    r"""
+    Temporary file fixture that can be reopened/closed and still
+    clean itself up afterwards.
+
+    Similar to the built-in ``tmpdir`` fixture, but safer for now:
+
+    * https://github.com/pytest-dev/pytest/issues/13669
+
+    """
+    from tempfile import NamedTemporaryFile
+    from os import unlink
+    t = NamedTemporaryFile(delete=False)
+    yield t
+    unlink(t.name)

src/doc/en/reference/libs/index.rst

@@ -89,10 +89,8 @@ GAP
 
    sage/libs/gap/context_managers
    sage/libs/gap/gap_functions
-   sage/libs/gap/test_long
    sage/libs/gap/util
    sage/libs/gap/libgap
-   sage/libs/gap/test
    sage/libs/gap/element
    sage/libs/gap/saved_workspace
 

src/sage/libs/gap/gap_test.py

@@ -0,0 +1,85 @@
+import pytest
+from sage.libs.gap.libgap import libgap
+
+
+def test_libgap_can_read_and_write_files(tmpfile):
+    """
+    Test that libgap can write to a temporary file and
+    subsequently read it.
+
+    See :issue:`16502`, :issue:`15833`.
+    """
+    message = "Ceci n'est pas une groupe"
+    libgap.PrintTo(tmpfile.name, message)
+    with open(tmpfile.name) as f:
+        contents = f.read()
+    assert contents == message
+    SystemFile = libgap.function_factory('StringFile')
+    assert SystemFile(tmpfile.name) == libgap(message)
+
+
+def test_gc_loop_1():
+    r"""
+    Stress test for garbage collection in libgap.
+
+    Manually runs the GAP garbage collector, and then creates 10,000
+    instances of the cyclic group of order two in a loop. In each
+    iteration, the python variable is overwritten, meaning that python
+    is free to garbage collect the object.
+    """
+    libgap.collect()
+    for _ in range(10000):
+        G = libgap.CyclicGroup(2)
+    assert True
+
+
+def test_gc_loop_2():
+    r"""
+    Stress test for garbage collection in libgap.
+
+    Create the free group on two elements (``a`` and ``b``) and then
+    construct a quotient group of order two in a loop by specifying
+    some relations. The python variables are overwritten in each
+    iteration, meaning that python is free to garbage-collect them.
+    (We also ensure that the quotient group has the expected order.)
+
+    After that loop, we take one of the generators of the quotient
+    group (from the final iteration), and compute its order in a
+    loop. The python reference from the final iteration lives on,
+    so this generator should not be collected.
+    """
+    G = libgap.FreeGroup(2)
+    a, b = G.GeneratorsOfGroup()
+    two = libgap(2)
+
+    for _ in range(100):
+        rel = libgap([a**2, b**2, a*b*a*b])
+        H = G / rel
+        H1 = H.GeneratorsOfGroup()[0]
+        n = H1.Order()
+        assert n == two
+
+    result = True
+    for i in range(300000):
+        n = libgap.Order(H1)
+        result &= (n == two)
+    assert result
+
+
+def test_gc_loop_3():
+    r"""
+    Stress test for garbage collection in libgap.
+
+    Create the free group on two elements (``a`` and ``b``) and then
+    add some of its elements to a list in a loop. A new, empty list is
+    created at each iteration, so this mainly serves to guarantee that
+    the generators of the group are not garbage-collected.
+    """
+    G = libgap.FreeGroup(2)
+    a, b = G.GeneratorsOfGroup()
+    for _ in range(300000):
+        lis = libgap([])
+        lis.Add(a ** 2)
+        lis.Add(b ** 2)
+        lis.Add(b * a)
+    assert True

src/sage/libs/gap/meson.build

@@ -8,11 +8,10 @@ py.install_sources(
   'gap_functions.py',
   'gap_globals.py',
   'gap_includes.pxd',
+  'gap_test.py',
   'operations.py',
   'sage.gaprc',
   'saved_workspace.py',
-  'test.py',
-  'test_long.py',
   'util.pxd',
   subdir: 'sage/libs/gap',
 )