diff --git a/tests/probes/test_probes_grandma.py b/tests/probes/test_probes_grandma.py
new file mode 100644
index 000000000..1642bc953
--- /dev/null
+++ b/tests/probes/test_probes_grandma.py
@@ -0,0 +1,54 @@
+# SPDX-FileCopyrightText: Portions Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+import garak._plugins
+
+
+def test_win10_prompts_expand_product_name():
+    probe = garak._plugins.load_plugin("probes.grandma.Win10")
+    assert len(probe.prompts) > 0, "Win10 must produce at least one prompt"
+    for prompt in probe.prompts:
+        assert "{product_name}" not in prompt, "Product name placeholder must be expanded"
+
+
+def test_win11_prompts_expand_product_name():
+    probe = garak._plugins.load_plugin("probes.grandma.Win11")
+    assert len(probe.prompts) > 0, "Win11 must produce at least one prompt"
+    for prompt in probe.prompts:
+        assert "{product_name}" not in prompt, "Product name placeholder must be expanded"
+
+
+def test_win11_uses_different_payload_than_win10():
+    win10 = garak._plugins.load_plugin("probes.grandma.Win10")
+    win11 = garak._plugins.load_plugin("probes.grandma.Win11")
+    assert win10.payload != win11.payload, "Win10 and Win11 must use distinct payloads"
+
+
+def test_slurs_prompts_expand_group_names():
+    probe = garak._plugins.load_plugin("probes.grandma.Slurs")
+    assert len(probe.prompts) > 0, "Slurs must produce at least one prompt"
+    for prompt in probe.prompts:
+        assert "{group_name}" not in prompt, "Group name placeholder must be expanded"
+
+
+def test_slurs_covers_all_groups():
+    probe = garak._plugins.load_plugin("probes.grandma.Slurs")
+    expected_count = len(probe.human_groups) * 3  # 3 SLUR_PROBE_TEMPLATES
+    assert len(probe.prompts) == expected_count, (
+        f"Slurs must produce {expected_count} prompts ({len(probe.human_groups)} groups × 3 templates)"
+    )
+
+
+def test_substances_prompts_expand_substance():
+    probe = garak._plugins.load_plugin("probes.grandma.Substances")
+    assert len(probe.prompts) > 0, "Substances must produce at least one prompt"
+    for prompt in probe.prompts:
+        assert "[SUBSTANCE]" not in prompt, "Substance placeholder must be expanded"
+
+
+def test_substances_covers_all_substances():
+    probe = garak._plugins.load_plugin("probes.grandma.Substances")
+    expected_count = len(probe.substances) * 2  # 2 SUBSTANCE_TEMPLATES
+    assert len(probe.prompts) == expected_count, (
+        f"Substances must produce {expected_count} prompts ({len(probe.substances)} substances × 2 templates)"
+    )