diff --git a/test/unit/test_extension_plugins.py b/test/unit/test_extension_plugins.py
new file mode 100644
index 00000000000..f03383bcfe0
--- /dev/null
+++ b/test/unit/test_extension_plugins.py
@@ -0,0 +1,132 @@
+import pytest
+
+from metaflow.extension_support import plugins as plugins_module
+from metaflow.extension_support.plugins import (
+    get_plugin,
+    get_plugin_name,
+    get_trampoline_cli_names,
+    merge_lists,
+)
+
+
+class TestMergeLists:
+    def test_overrides_win_over_base(self):
+        class Item:
+            def __init__(self, name):
+                self.name = name
+
+        base = [Item("a"), Item("b"), Item("c")]
+        overrides = [Item("b_new"), Item("d")]
+        merge_lists(base, overrides, "name")
+
+        names = [item.name for item in base]
+        assert "b_new" in names
+        assert "d" in names
+        assert "a" in names
+        assert "c" in names
+
+    def test_empty_overrides_keeps_base(self):
+        class Item:
+            def __init__(self, name):
+                self.name = name
+
+        base = [Item("a"), Item("b")]
+        overrides = []
+        merge_lists(base, overrides, "name")
+
+        names = [item.name for item in base]
+        assert names == ["a", "b"]
+
+    def test_empty_base_uses_overrides(self):
+        class Item:
+            def __init__(self, name):
+                self.name = name
+
+        base = []
+        overrides = [Item("x"), Item("y")]
+        merge_lists(base, overrides, "name")
+
+        names = [item.name for item in base]
+        assert names == ["x", "y"]
+
+    def test_both_empty(self):
+        base = []
+        overrides = []
+        merge_lists(base, overrides, "name")
+        assert base == []
+
+    def test_no_duplicates_in_result(self):
+        class Item:
+            def __init__(self, name):
+                self.name = name
+
+        base = [Item("a"), Item("b")]
+        overrides = [Item("a"), Item("b")]
+        merge_lists(base, overrides, "name")
+
+        names = set(item.name for item in base)
+        assert names == {"a", "b"}
+
+
+class TestGetPluginName:
+    def test_step_decorator_name_extraction(self):
+        class MockDecorator:
+            name = "my_decorator"
+
+        assert get_plugin_name("step_decorator", MockDecorator()) == "my_decorator"
+
+    def test_environment_type_extraction(self):
+        class MockEnv:
+            TYPE = "conda"
+
+        assert get_plugin_name("environment", MockEnv()) == "conda"
+
+    def test_sidecar_returns_none(self):
+        class MockSidecar:
+            pass
+
+        assert get_plugin_name("sidecar", MockSidecar()) is None
+
+    def test_cli_single_command(self):
+        class MockCLI:
+            commands = {"run"}
+
+        assert get_plugin_name("cli", MockCLI()) == "run"
+
+    def test_cli_too_many_commands(self):
+        class MockCLI:
+            commands = {"run", "step", "start"}
+
+        result = get_plugin_name("cli", MockCLI())
+        assert "too many commands" in result
+
+    def test_unknown_category_raises_key_error(self):
+        class MockPlugin:
+            name = "test"
+
+        with pytest.raises(KeyError):
+            get_plugin_name("nonexistent_category", MockPlugin())
+
+
+class TestGetPlugin:
+    def test_get_plugin_raises_value_error_for_invalid_path(self):
+        with pytest.raises(ValueError, match="Cannot locate"):
+            get_plugin("step_decorator", "nonexistent.module.path.FakeClass", "fake")
+
+    def test_get_plugin_successfully_loads_real_class(self):
+        cls = get_plugin(
+            "step_decorator",
+            "metaflow.plugins.retry_decorator.RetryDecorator",
+            "retry",
+        )
+        assert cls.name == "retry"
+
+
+class TestGetTrampolineCliNames:
+    def test_returns_frozenset(self):
+        result = get_trampoline_cli_names()
+        assert isinstance(result, frozenset)
+
+    def test_contains_expected_entries(self):
+        result = get_trampoline_cli_names()
+        assert "batch" in result or "kubernetes" in result