Add tests for the mainline.

src/briefcase/__main__.py

@@ -1,5 +1,6 @@
 import sys
 from contextlib import suppress
+from pathlib import Path
 
 from briefcase.cmdline import parse_cmdline
 from briefcase.console import Console, Log
@@ -16,7 +17,7 @@ def main():
         command = Command(logger=logger, console=console)
         options = command.parse_options(extra=extra_cmdline)
         command.check_obsolete_data_dir()
-        command.parse_config("pyproject.toml")
+        command.parse_config(Path.cwd() / "pyproject.toml")
         command(**options)
     except HelpText as e:
         logger.info()
@@ -41,8 +42,8 @@ def main():
         with suppress(KeyboardInterrupt):
             logger.save_log_to_file(command)
 
-    sys.exit(result)
+    return result
 
 
 if __name__ == "__main__":
-    main()
+    sys.exit(main())  # pragma: no cover

src/briefcase/commands/base.py

@@ -117,7 +117,7 @@ def __init__(
         console: Console,
         tools: ToolCache = None,
         apps: dict = None,
-        base_path: Path = Path.cwd(),
+        base_path: Path = None,
         data_path: Path = None,
         is_clone: bool = False,
     ):
@@ -132,7 +132,10 @@ def __init__(
         :param is_clone: Flag that Command was triggered by the user's requested Command;
             for instance, RunCommand can invoke UpdateCommand and/or BuildCommand.
         """
-        self.base_path = Path(base_path)
+        if base_path is None:
+            self.base_path = Path.cwd()
+        else:
+            self.base_path = base_path
         self.data_path = self.validate_data_path(data_path)
         self.apps = {} if apps is None else apps
         self.is_clone = is_clone

tests/test_mainline.py

@@ -0,0 +1,159 @@
+import sys
+from pathlib import Path
+
+import pytest
+
+from briefcase.__main__ import main
+from briefcase.commands.create import CreateCommand
+
+from .utils import create_file
+
+
+@pytest.fixture
+def pyproject_toml(monkeypatch, tmp_path):
+    # Monkeypatch cwd() to use a test folder.
+    monkeypatch.setattr(Path, "cwd", lambda: tmp_path)
+
+    create_file(
+        tmp_path / "pyproject.toml",
+        """
+[build-system]
+requires = ["briefcase"]
+
+[tool.briefcase]
+project_name = "Hello World"
+bundle = "com.example"
+version = "0.0.1"
+
+[tool.briefcase.app.myapp]
+description = "My first application"
+sources = ["myapp"]
+
+    """,
+    )
+
+
+def test_help(monkeypatch, tmp_path, capsys):
+    "Briefcase can output help."
+    # Set the test command line
+    monkeypatch.setattr(sys, "argv", ["briefcase", "--help"])
+
+    # Help has a return code of -10
+    assert main() == -10
+
+    output = capsys.readouterr().out
+    assert output.startswith(
+        "\nusage: briefcase [-h] <command> [<platform>] [<format>] ...\n"
+    )
+
+    # No log file was written
+    assert len(list(tmp_path.glob("briefcase.*.log"))) == 0
+
+
+def test_command(monkeypatch, tmp_path, capsys):
+    "A command can be successful"
+    # Monkeypatch cwd() to use a test folder.
+    monkeypatch.setattr(Path, "cwd", lambda: tmp_path)
+
+    # Create a dummy empty template to use in the new command
+    create_file(tmp_path / "template" / "cookiecutter.json", '{"app_name": "app_name"}')
+    create_file(
+        tmp_path / "template" / "{{ cookiecutter.app_name }}" / "app", "content"
+    )
+
+    # Set the test command line
+    monkeypatch.setattr(
+        sys,
+        "argv",
+        ["briefcase", "new", "--no-input", "--template", str(tmp_path / "template")],
+    )
+
+    # Successful return is 0
+    assert main() == 0
+
+    output = capsys.readouterr().out
+    assert output.startswith("\nGenerating a new application 'Hello World'\n")
+
+    # No log file was written
+    assert len(list(tmp_path.glob("briefcase.*.log"))) == 0
+
+
+def test_command_error(monkeypatch, tmp_path, capsys):
+    "A command can raise a known error"
+    # Monkeypatch cwd() to use a test folder.
+    monkeypatch.setattr(Path, "cwd", lambda: tmp_path)
+
+    # Set the test command line
+    monkeypatch.setattr(sys, "argv", ["briefcase", "create"])
+
+    # Help has a return code of -10
+    assert main() == 100
+
+    output = capsys.readouterr().out
+    assert output.startswith(
+        "\nBriefcase configuration error: Configuration file not found."
+    )
+
+    # A log file was written
+    assert len(list(tmp_path.glob("briefcase.*.create.log"))) == 1
+
+
+def test_unknown_command_error(monkeypatch, pyproject_toml, capsys):
+    "A command can raise an unknown error"
+    monkeypatch.setattr(sys, "argv", ["briefcase", "create"])
+
+    # Monkeypatch an error into the create command
+    def bad_generate_app_template(self, app):
+        raise ValueError("Bad value")
+
+    monkeypatch.setattr(
+        CreateCommand, "generate_app_template", bad_generate_app_template
+    )
+
+    # Error is surfaced to the user
+    with pytest.raises(ValueError, match=r"Bad value"):
+        main()
+
+
+def test_interrupted_command(monkeypatch, pyproject_toml, tmp_path, capsys):
+    "A command can be interrupted"
+    monkeypatch.setattr(sys, "argv", ["briefcase", "create"])
+
+    # Monkeypatch a keyboard interrupt into the create command
+    def interrupted_generate_app_template(self, app):
+        raise KeyboardInterrupt()
+
+    monkeypatch.setattr(
+        CreateCommand, "generate_app_template", interrupted_generate_app_template
+    )
+
+    # Interrupted command return -42
+    assert main() == -42
+
+    output = capsys.readouterr().out
+    assert "\nAborted by user.\n" in output
+
+    # No log file was written
+    assert len(list(tmp_path.glob("briefcase.*.create.log"))) == 0
+
+
+def test_interrupted_command_with_log(monkeypatch, pyproject_toml, tmp_path, capsys):
+    "A log can be generated when a command is interrupted"
+    monkeypatch.setattr(sys, "argv", ["briefcase", "create", "--log"])
+
+    # Monkeypatch a keyboard interrupt into the create command
+    def interrupted_generate_app_template(self, app):
+        raise KeyboardInterrupt()
+
+    monkeypatch.setattr(
+        CreateCommand, "generate_app_template", interrupted_generate_app_template
+    )
+
+    # Interrupted command return -42
+    assert main() == -42
+
+    output = capsys.readouterr().out
+    assert "\nAborted by user.\n" in output
+
+    # A log file was written
+    assert len(list(tmp_path.glob("briefcase.*.create.log"))) == 1