test: add CLI test for flattener

tests/conftest.py

@@ -9,6 +9,7 @@
 import ape
 import pytest
 import vvm  # type: ignore
+from click.testing import CliRunner
 
 # NOTE: Ensure that we don't use local paths for these
 DATA_FOLDER = Path(mkdtemp()).resolve()
@@ -211,6 +212,11 @@ def all_versions():
     return ALL_VERSIONS
 
 
+@pytest.fixture
+def cli_runner():
+    return CliRunner()
+
+
 def _get_tb_contract(version: str, project, account):
     registry_type = project.get_contract(f"registry_{version}")
     registry = account.deploy(registry_type)

tests/test_cli.py

@@ -0,0 +1,31 @@
+from pathlib import Path
+from tempfile import NamedTemporaryFile
+
+import pytest
+
+from ape_vyper._cli import cli
+
+
+@pytest.mark.parametrize(
+    "contract_name,expected",
+    [
+        # This first one has most known edge cases
+        (
+            "flatten_me.vy",
+            [
+                "from vyper.interfaces import ERC20",
+                "interface Dep:",
+                "interface IFace:",
+                "interface IFaceTwo:",
+            ],
+        ),
+    ],
+)
+def test_cli_flatten(project, contract_name, expected, cli_runner):
+    path = project.contracts_folder / contract_name
+    with NamedTemporaryFile() as tmpfile:
+        result = cli_runner.invoke(cli, ["flatten", str(path), tmpfile.name])
+        assert result.exit_code == 0, result.stderr_bytes
+        output = Path(tmpfile.name).read_text()
+        for expect in expected:
+            assert expect in output