Added test that example updates ok

tests/test_example.py

@@ -1,8 +1,10 @@
+import functools
 import shlex
 import subprocess
 from pathlib import Path
 
 import pytest
+import yaml
 from copier import run_copy
 from prompt_toolkit.validation import ValidationError
 
@@ -34,28 +36,53 @@ def copy_project(
     )
 
 
-def test_template(tmp_path: Path):
-    project = tmp_path / "project"
-    venv = tmp_path / "venv"
-    copy_project(project)
+def run_pipe(cmd: str, cwd=None):
+    sp = subprocess.run(
+        shlex.split(cmd),
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+        cwd=cwd,
+    )
+    output = sp.stdout.decode()
+    assert sp.returncode == 0, output
+    return output
 
-    def run(cmd: str):
-        sp = subprocess.run(
-            shlex.split(cmd),
-            stdout=subprocess.PIPE,
-            stderr=subprocess.STDOUT,
-            cwd=str(project),
-        )
-        assert sp.returncode == 0, sp.stdout.decode()
 
-    run(f"python -m venv {venv}")
-    run(f"{venv}/bin/python -m pip install -e .[dev]")
-    run(f"{venv}/bin/tox -p")
+def test_template(tmp_path: Path):
+    project_path = tmp_path / "project"
+    venv_path = tmp_path / "venv"
+    copy_project(project_path)
+    run = functools.partial(run_pipe, cwd=str(project_path))
+    run(f"python -m venv {venv_path}")
+    run(f"{venv_path}/bin/python -m pip install -e .[dev]")
+    run(f"{venv_path}/bin/tox -p")
 
 
 def test_bad_repo_name(tmp_path: Path):
     with pytest.raises(ValidationError, match="bad:thing is not a valid repo name"):
         copy_project(tmp_path, repo_name="bad:thing")
 
 
+def test_example_repo_updates(tmp_path: Path):
+    generated_path = tmp_path / "generated"
+    example_url = (
+        "https://github.com/DiamondLightSource/python-copier-template-example.git"
+    )
+    example_path = tmp_path / "example"
+    copy_project(generated_path)
+    run_pipe(f"git clone {example_url} {example_path}")
+    with open(example_path / ".copier-answers.yml") as f:
+        d = yaml.safe_load(f)
+    d["_src_path"] = str(TOP)
+    with open(example_path / ".copier-answers.yml", "w") as f:
+        yaml.dump(d, f)
+    run_pipe(f"git -C {example_path} commit -am 'Update src'")
+    run_pipe(f"copier update --trust --vcs-ref=HEAD -A {example_path}")
+    output = run_pipe(
+        "diff -ur --exclude=.git --ignore-matching-lines='_commit: '"
+        f" {generated_path} {example_path}"
+    )
+    assert not output, output
+
+
 # TODO: check that copier update python-copier-template-example matches generated