Refactored test_build.py (#565)

* Refactored test_build.py

Made use of more generic with_[git_]project decorators.

Co-authored-by: Adi Roiban <adiroiban@gmail.com>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: Adi Roiban <adiroiban@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/towncrier/newsfragments/562.misc

@@ -0,0 +1 @@
+Improved structure and readability of some tests for building the changelog.

src/towncrier/test/helpers.py

@@ -5,6 +5,7 @@
 
 from functools import wraps
 from pathlib import Path
+from subprocess import call
 from typing import Any, Callable
 
 from click.testing import CliRunner
@@ -62,10 +63,83 @@ def setup_simple_project(
 ) -> None:
     if config is None:
         config = "[tool.towncrier]\n" 'package = "foo"\n' + extra_config
-
+    else:
+        config = textwrap.dedent(config)
     Path(pyproject_path).write_text(config)
     Path("foo").mkdir()
     Path("foo/__init__.py").write_text('__version__ = "1.2.3"\n')
 
     if mkdir_newsfragments:
         Path("foo/newsfragments").mkdir()
+
+
+def with_project(
+    *,
+    config: str | None = None,
+    pyproject_path: str = "pyproject.toml",
+) -> Callable[[Callable[..., Any]], Callable[..., Any]]:
+    """Decorator to run a test with an isolated directory containing a simple
+    project.
+
+    The files are not managed by git.
+
+    `config` is the content of the config file.
+    It will be automatically dedented.
+
+    `pyproject_path` is the path where to store the config file.
+    """
+
+    def decorator(fn: Callable[..., Any]) -> Callable[..., Any]:
+        @wraps(fn)
+        def test(*args: Any, **kw: Any) -> Any:
+            runner = CliRunner()
+            with runner.isolated_filesystem():
+                setup_simple_project(
+                    config=config,
+                    pyproject_path=pyproject_path,
+                )
+
+                return fn(*args, runner=runner, **kw)
+
+        return test
+
+    return decorator
+
+
+def with_git_project(
+    *,
+    config: str | None = None,
+    pyproject_path: str = "pyproject.toml",
+) -> Callable[[Callable[..., Any]], Callable[..., Any]]:
+    """Decorator to run a test with an isolated directory containing a simple
+    project checked into git.
+    Use `config` to tweak the content of the config file.
+    Use `pyproject_path` to tweak the location of the config file.
+    """
+
+    def decorator(fn: Callable[..., Any]) -> Callable[..., Any]:
+        def _commit() -> None:
+            call(["git", "add", "."])
+            call(["git", "commit", "-m", "Second Commit"])
+
+        @wraps(fn)
+        def test(*args: Any, **kw: Any) -> Any:
+            runner = CliRunner()
+            with runner.isolated_filesystem():
+                setup_simple_project(
+                    config=config,
+                    pyproject_path=pyproject_path,
+                )
+
+                call(["git", "init"])
+                call(["git", "config", "user.name", "user"])
+                call(["git", "config", "user.email", "user@example.com"])
+                call(["git", "config", "commit.gpgSign", "false"])
+                call(["git", "add", "."])
+                call(["git", "commit", "-m", "Initial Commit"])
+
+                return fn(*args, runner=runner, commit=_commit, **kw)
+
+        return test
+
+    return decorator