diff --git a/tests/test_add_schematic_component.py b/tests/test_add_schematic_component.py
new file mode 100644
index 0000000..dff0227
--- /dev/null
+++ b/tests/test_add_schematic_component.py
@@ -0,0 +1,191 @@
+"""
+Tests for add_schematic_component handler, focusing on the unit parameter
+for multi-unit symbols (e.g. quad optocouplers, dual op-amps).
+"""
+
+import re
+import shutil
+import sys
+import tempfile
+from pathlib import Path
+from typing import Any
+
+import pytest
+
+sys.path.insert(0, str(Path(__file__).parent.parent / "python"))
+
+TEMPLATES_DIR = Path(__file__).parent.parent / "python" / "templates"
+EMPTY_SCH = TEMPLATES_DIR / "empty.kicad_sch"
+
+
+def _write_temp_sch(content: str) -> Path:
+    tmp = tempfile.NamedTemporaryFile(
+        suffix=".kicad_sch", delete=False, mode="w", encoding="utf-8"
+    )
+    tmp.write(content)
+    tmp.close()
+    return Path(tmp.name)
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+
+def _unit_values_in_file(path: Path) -> list[int]:
+    """Return all (unit N) values written for symbol instances in the schematic."""
+    content = path.read_text()
+    # Match top-level symbol instances: (symbol (lib_id ...) (at ...) (unit N) ...)
+    return [int(n) for n in re.findall(r"\(symbol \(lib_id [^)]+\) \(at [^)]+\) \(unit (\d+)\)", content)]
+
+
+# ---------------------------------------------------------------------------
+# Unit tests – create_component_instance
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.unit
+class TestCreateComponentInstanceUnit:
+    """Tests for DynamicSymbolLoader.create_component_instance unit parameter."""
+
+    def setup_method(self) -> None:
+        from commands.dynamic_symbol_loader import DynamicSymbolLoader
+
+        self.DynamicSymbolLoader = DynamicSymbolLoader
+
+    def _loader(self) -> Any:
+        return self.DynamicSymbolLoader()
+
+    def test_default_unit_is_1(self, tmp_path: Any) -> None:
+        sch = tmp_path / "test.kicad_sch"
+        shutil.copy(EMPTY_SCH, sch)
+        loader = self._loader()
+        loader.create_component_instance(
+            sch, "Device", "R", reference="R1", value="10k", x=10, y=10
+        )
+        units = _unit_values_in_file(sch)
+        assert 1 in units
+
+    def test_explicit_unit_1(self, tmp_path: Any) -> None:
+        sch = tmp_path / "test.kicad_sch"
+        shutil.copy(EMPTY_SCH, sch)
+        loader = self._loader()
+        loader.create_component_instance(
+            sch, "Device", "R", reference="R1", value="10k", x=10, y=10, unit=1
+        )
+        units = _unit_values_in_file(sch)
+        assert units.count(1) >= 1
+
+    def test_unit_2_written_correctly(self, tmp_path: Any) -> None:
+        sch = tmp_path / "test.kicad_sch"
+        shutil.copy(EMPTY_SCH, sch)
+        loader = self._loader()
+        loader.create_component_instance(
+            sch, "Device", "R", reference="U1", value="TLP291-4", x=10, y=10, unit=2
+        )
+        units = _unit_values_in_file(sch)
+        assert 2 in units
+
+    def test_unit_4_written_correctly(self, tmp_path: Any) -> None:
+        sch = tmp_path / "test.kicad_sch"
+        shutil.copy(EMPTY_SCH, sch)
+        loader = self._loader()
+        loader.create_component_instance(
+            sch, "Device", "R", reference="U1", value="TLP291-4", x=10, y=10, unit=4
+        )
+        units = _unit_values_in_file(sch)
+        assert 4 in units
+
+    def test_instances_block_uses_same_unit(self, tmp_path: Any) -> None:
+        """The (instances ...) path block must also record the correct unit number."""
+        sch = tmp_path / "test.kicad_sch"
+        shutil.copy(EMPTY_SCH, sch)
+        loader = self._loader()
+        loader.create_component_instance(
+            sch, "Device", "R", reference="U1", value="val", x=5, y=5, unit=3
+        )
+        content = sch.read_text()
+        # The (unit 3) inside the (instances ...) block
+        assert "(unit 3)" in content
+        # Count occurrences — should appear at least twice (symbol header + instances)
+        assert content.count("(unit 3)") >= 2
+
+    def test_multiple_units_same_reference(self, tmp_path: Any) -> None:
+        """Placing units A and B of the same reference produces two distinct unit entries."""
+        sch = tmp_path / "test.kicad_sch"
+        shutil.copy(EMPTY_SCH, sch)
+        loader = self._loader()
+        loader.create_component_instance(
+            sch, "Device", "R", reference="U10", value="TLP291-4", x=10, y=10, unit=1
+        )
+        loader.create_component_instance(
+            sch, "Device", "R", reference="U10", value="TLP291-4", x=10, y=35, unit=2
+        )
+        units = _unit_values_in_file(sch)
+        assert 1 in units
+        assert 2 in units
+
+
+# ---------------------------------------------------------------------------
+# Handler-level tests – _handle_add_schematic_component
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.unit
+class TestHandlerAddSchematicComponent:
+    """Tests for KiCADInterface._handle_add_schematic_component unit plumbing."""
+
+    def _call_handler(self, params: dict) -> dict:
+        from kicad_interface import KiCADInterface
+
+        iface = KiCADInterface()
+        return iface._handle_add_schematic_component(params)
+
+    def test_missing_schematic_path_returns_error(self) -> None:
+        result = self._call_handler({"component": {"type": "R", "library": "Device"}})
+        assert result["success"] is False
+        assert "path" in result["message"].lower() or "schematic" in result["message"].lower()
+
+    def test_missing_component_returns_error(self, tmp_path: Any) -> None:
+        sch = tmp_path / "test.kicad_sch"
+        shutil.copy(EMPTY_SCH, sch)
+        result = self._call_handler({"schematicPath": str(sch)})
+        assert result["success"] is False
+
+    def test_unit_defaults_to_1_in_handler(self, tmp_path: Any) -> None:
+        sch = tmp_path / "test.kicad_sch"
+        shutil.copy(EMPTY_SCH, sch)
+        result = self._call_handler({
+            "schematicPath": str(sch),
+            "component": {
+                "library": "Device",
+                "type": "R",
+                "reference": "R99",
+                "value": "1k",
+                "x": 10,
+                "y": 10,
+                # no "unit" key — should default to 1
+            },
+        })
+        assert result["success"] is True
+        units = _unit_values_in_file(sch)
+        assert 1 in units
+
+    def test_unit_2_passed_through_handler(self, tmp_path: Any) -> None:
+        sch = tmp_path / "test.kicad_sch"
+        shutil.copy(EMPTY_SCH, sch)
+        result = self._call_handler({
+            "schematicPath": str(sch),
+            "component": {
+                "library": "Device",
+                "type": "R",
+                "reference": "U10",
+                "value": "TLP291-4",
+                "x": 25,
+                "y": 35,
+                "unit": 2,
+            },
+        })
+        assert result["success"] is True
+        units = _unit_values_in_file(sch)
+        assert 2 in units