diff --git a/tests/test_external_editor_integration.py b/tests/test_external_editor_integration.py
new file mode 100644
index 0000000..bef780d
--- /dev/null
+++ b/tests/test_external_editor_integration.py
@@ -0,0 +1,114 @@
+"""Integration tests for external editor - launches real editors."""
+import os
+import tempfile
+import pytest
+from unittest.mock import patch, MagicMock
+from src.external_editor import (
+    ExternalEditorLauncher,
+    ExternalEditorConfig,
+    TextEditorConfig,
+    create_temp_modified_file,
+)
+
+
+@pytest.fixture
+def vscode_editor():
+    return TextEditorConfig(name="vscode", path="code.exe", diff_args=["--diff"])
+
+
+@pytest.fixture
+def ext_config(vscode_editor):
+    return ExternalEditorConfig(editors={"vscode": vscode_editor}, default_editor="vscode")
+
+
+@pytest.fixture
+def launcher(ext_config):
+    return ExternalEditorLauncher(ext_config)
+
+
+class TestExternalEditorIntegration:
+    def test_create_temp_modified_file_creates_valid_file(self):
+        content = "line1\nline2\nline3\n"
+        path = create_temp_modified_file(content)
+        try:
+            assert os.path.exists(path)
+            with open(path, encoding="utf-8") as f:
+                assert f.read() == content
+        finally:
+            if os.path.exists(path):
+                os.unlink(path)
+
+    def test_build_diff_command_format(self, launcher, vscode_editor):
+        cmd = launcher.build_diff_command(vscode_editor, "original.txt", "modified.txt")
+        assert cmd == ["code.exe", "--diff", "original.txt", "modified.txt"]
+
+    @patch("subprocess.Popen")
+    def test_launch_diff_calls_subprocess(self, mock_popen, launcher):
+        mock_popen.return_value = MagicMock()
+        result = launcher.launch_diff("vscode", "orig.txt", "mod.txt")
+        assert result is not None
+        mock_popen.assert_called_once_with(["code.exe", "--diff", "orig.txt", "mod.txt"])
+
+    @patch("subprocess.Popen")
+    def test_launch_diff_with_real_files(self, mock_popen, launcher):
+        mock_popen.return_value = MagicMock()
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".txt", delete=False, encoding="utf-8") as f:
+            f.write("original content\n")
+            orig_path = f.name
+        try:
+            mod_path = create_temp_modified_file("modified content\n")
+            try:
+                result = launcher.launch_diff("vscode", orig_path, mod_path)
+                assert result is not None
+                call_args = mock_popen.call_args[0][0]
+                assert call_args[0] == "code.exe"
+                assert call_args[1] == "--diff"
+                assert call_args[2] == orig_path
+                assert call_args[3] == mod_path
+            finally:
+                if os.path.exists(mod_path):
+                    os.unlink(mod_path)
+        finally:
+            if os.path.exists(orig_path):
+                os.unlink(orig_path)
+
+
+class TestExternalEditorWithRealVSCode:
+    @pytest.mark.skipif(
+        os.environ.get("TEST_REAL_VSCODE") != "1",
+        reason="Set TEST_REAL_VSCODE=1 environment variable to run this test"
+    )
+    def test_launch_real_vscode_diff(self):
+        vscode_path = os.environ.get("VSCODE_PATH", "code.exe")
+        if not os.path.exists(vscode_path) and vscode_path == "code.exe":
+            import shutil
+            if not shutil.which("code"):
+                pytest.skip("VSCode not found in PATH")
+        config = ExternalEditorConfig(
+            editors={"vscode": TextEditorConfig(name="vscode", path=vscode_path, diff_args=["--diff"])},
+            default_editor="vscode"
+        )
+        launcher = ExternalEditorLauncher(config)
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".txt", delete=False, encoding="utf-8") as f:
+            f.write("line1\nline2\nline3\n")
+            orig_path = f.name
+        try:
+            mod_path = create_temp_modified_file("line1\nmodified line2\nline3\n")
+            try:
+                import subprocess
+                proc = launcher.launch_diff("vscode", orig_path, mod_path)
+                assert proc is not None
+                import time
+                time.sleep(1)
+                proc.terminate()
+                proc.wait(timeout=5)
+            finally:
+                if os.path.exists(mod_path):
+                    os.unlink(mod_path)
+        finally:
+            if os.path.exists(orig_path):
+                os.unlink(orig_path)
+
+
+if __name__ == "__main__":
+    pytest.main([__file__, "-v"])