Do not assume that the test directory is writeable

brian2/tests/test_functions.py

@@ -1,4 +1,6 @@
 import os
+import shutil
+import tempfile
 
 import pytest
 from numpy.testing import assert_equal
@@ -698,32 +700,37 @@ def foo(x, y):
 def test_external_function_cpp_standalone():
     set_device("cpp_standalone", directory=None)
     this_dir = os.path.abspath(os.path.dirname(__file__))
+    with tempfile.TemporaryDirectory(prefix="brian_testsuite_") as tmpdir:
+        # copy the test function to the temporary directory
+        # this avoids issues with the file being in a directory that is not writable
+        shutil.copy(os.path.join(this_dir, "func_def_cpp.h"), tmpdir)
+        shutil.copy(os.path.join(this_dir, "func_def_cpp.cpp"), tmpdir)
+
+        @implementation(
+            "cpp",
+            "//all code in func_def_cpp.cpp",
+            headers=['"func_def_cpp.h"'],
+            include_dirs=[tmpdir],
+            sources=[os.path.join(tmpdir, "func_def_cpp.cpp")],
+        )
+        @check_units(x=volt, y=volt, result=volt)
+        def foo(x, y):
+            return x + y + 3 * volt
 
-    @implementation(
-        "cpp",
-        "//all code in func_def_cpp.cpp",
-        headers=['"func_def_cpp.h"'],
-        include_dirs=[this_dir],
-        sources=[os.path.join(this_dir, "func_def_cpp.cpp")],
-    )
-    @check_units(x=volt, y=volt, result=volt)
-    def foo(x, y):
-        return x + y + 3 * volt
-
-    G = NeuronGroup(
-        1,
-        """
-        func = foo(x, y) : volt
-        x : volt
-        y : volt
-        """,
-    )
-    G.x = 1 * volt
-    G.y = 2 * volt
-    mon = StateMonitor(G, "func", record=True)
-    net = Network(G, mon)
-    net.run(defaultclock.dt)
-    assert mon[0].func == [6] * volt
+        G = NeuronGroup(
+            1,
+            """
+            func = foo(x, y) : volt
+            x : volt
+            y : volt
+            """,
+        )
+        G.x = 1 * volt
+        G.y = 2 * volt
+        mon = StateMonitor(G, "func", record=True)
+        net = Network(G, mon)
+        net.run(defaultclock.dt)
+        assert mon[0].func == [6] * volt
 
 
 @pytest.mark.codegen_independent