diff --git a/raster/r.null/tests/r_null_test.py b/raster/r.null/tests/r_null_test.py
new file mode 100644
index 00000000000..c31487f4d3c
--- /dev/null
+++ b/raster/r.null/tests/r_null_test.py
@@ -0,0 +1,59 @@
+import os
+
+import pytest
+
+import grass.script as gs
+from grass.tools import Tools
+
+
+@pytest.fixture
+def session_with_maps(tmp_path):
+    """A GRASS session with small rasters for r.null.
+
+    map_basic: integer categories 1, 2, 3 by row
+    map_fill_nulls: NULL, 2, 3 by row
+    map_float: floating point values 1, 2.5, 3 by row
+    """
+    project = tmp_path / "r_null_project"
+    gs.create_project(project)
+    with gs.setup.init(project, env=os.environ.copy()) as session:
+        tools = Tools(session=session)
+        tools.g_region(n=3, s=0, e=3, w=0, res=1)
+        tools.r_mapcalc(expression="map_basic = row()")
+        tools.r_mapcalc(
+            expression="map_fill_nulls = if(row() == 1, null(), if(row() == 2, 2, 3))"
+        )
+        tools.r_mapcalc(
+            expression="map_float = if(row() == 1, 1, if(row() == 2, 2.5, 3))"
+        )
+        yield session
+
+
+def test_setnull_integer(session_with_maps):
+    """Cells matching setnull become NULL in an integer map (-i)."""
+    tools = Tools(session=session_with_maps)
+
+    tools.r_null(map="map_basic", setnull=1, flags="i")
+
+    described = tools.r_describe(map="map_basic", format="json", flags="1").json
+    assert described == {"has_nulls": True, "values": [2, 3]}
+
+
+def test_setnull_float(session_with_maps):
+    """Cells matching setnull become NULL in a floating point map (-f)."""
+    tools = Tools(session=session_with_maps)
+
+    tools.r_null(map="map_float", setnull=1, flags="f")
+
+    described = tools.r_describe(map="map_float", format="json", flags="r").json
+    assert described == {"has_nulls": True, "ranges": [{"min": 2.5, "max": 3}]}
+
+
+def test_fill_nulls(session_with_maps):
+    """NULL cells are replaced by the null= value."""
+    tools = Tools(session=session_with_maps)
+
+    tools.r_null(map="map_fill_nulls", null=1)
+
+    described = tools.r_describe(map="map_fill_nulls", format="json", flags="1").json
+    assert described == {"has_nulls": False, "values": [1, 2, 3]}
diff --git a/raster/r.null/testsuite/test_r_null.py b/raster/r.null/testsuite/test_r_null.py
deleted file mode 100644
index 8532a246f18..00000000000
--- a/raster/r.null/testsuite/test_r_null.py
+++ /dev/null
@@ -1,87 +0,0 @@
-import grass.script as gs
-from grass.gunittest.case import TestCase
-from grass.gunittest.main import test
-from grass.gunittest.gmodules import SimpleModule
-
-
-class TestRNull(TestCase):
-    """Test case for r.null module"""
-
-    @classmethod
-    def setUpClass(cls):
-        """Set up a temporary region and create test raster maps"""
-        cls.use_temp_region()
-        cls.runModule("g.region", n=3, s=0, e=3, w=0, res=1)
-
-        # Create map1: categories 1, 2, 3 as rows
-        cls.runModule(
-            "r.mapcalc",
-            expression="map_basic = row()",
-            overwrite=True,
-        )
-
-        # Create map1: categories null, 2, 3 as rows
-        cls.runModule(
-            "r.mapcalc",
-            expression="map_fill_nulls = if(row() == 1, null(), if(row() == 2, 2, if(row() == 3, 3, null())))",
-            overwrite=True,
-        )
-
-        # Create map1: categories 1, 2.5, 3 as rows
-        cls.runModule(
-            "r.mapcalc",
-            expression="map2 = if(row() == 1, 1, if(row() == 2, 2.5, if(row() == 3, 3, null())))",
-            overwrite=True,
-        )
-
-    @classmethod
-    def tearDownClass(cls):
-        """Remove temporary maps and region"""
-        cls.runModule(
-            "g.remove",
-            flags="f",
-            type="raster",
-            name=["map_basic", "map_fill_nulls", "map2"],
-        )
-        cls.del_temp_region()
-
-    def test_basic(self):
-        """Verify module execute with -i flag"""
-        module = SimpleModule("r.null", map="map_basic", setnull="1", flags="i")
-        self.assertModule(module)
-
-        # Validate category mappings using r.category
-        category_output = gs.parse_command(
-            "r.describe", map="map_basic", format="json", flags="1"
-        )
-        expected_output = {"has_nulls": True, "values": [2, 3]}
-
-        self.assertEqual(category_output, expected_output)
-
-    def test_float_flag(self):
-        """Verify module execute with -f flag"""
-        module = SimpleModule("r.null", map="map2", setnull="1", flags="f")
-        self.assertModule(module)
-
-        category_output = gs.parse_command(
-            "r.describe", map="map2", format="json", flags="r"
-        )
-        expected_output = {"has_nulls": True, "ranges": [{"min": 2.5, "max": 3}]}
-
-        self.assertEqual(category_output, expected_output)
-
-    def test_fill_nulls(self):
-        """Verify module fills nulls"""
-        module = SimpleModule("r.null", map="map_fill_nulls", null="1")
-        self.assertModule(module)
-
-        category_output = gs.parse_command(
-            "r.describe", map="map_fill_nulls", format="json", flags="1"
-        )
-        expected_output = {"has_nulls": False, "values": [1, 2, 3]}
-
-        self.assertEqual(category_output, expected_output)
-
-
-if __name__ == "__main__":
-    test()