Use system-agnostic command for running Python and devnull

In this commit, we use Ptrhon standard library to provide sys.executable and os.devnull.

tests/project_helpers.py

@@ -1,6 +1,7 @@
 """Common helpers shared between test_real_project and test_sample_projects."""
 import hashlib
 import logging
+import os
 import shlex
 import subprocess
 import sys
@@ -150,7 +151,7 @@ def venv_hash(self) -> str:
         The Python version currently used to run the tests is used to compute
         the hash and create the venv.
         """
-        dummy_script = self.venv_script_lines(Path("/dev/null"))
+        dummy_script = self.venv_script_lines(Path(os.devnull))
         py_version = f"{sys.version_info.major},{sys.version_info.minor}"
         script_and_version_bytes = ("".join(dummy_script) + py_version).encode()
         return hashlib.sha256(script_and_version_bytes).hexdigest()

tests/test_cmdline_options.py

@@ -192,7 +192,7 @@ def test_options_interactions__correct_options__does_not_abort(cli_arguments):
     )
     args = basepath + drawn_args
 
-    with open("/dev/null", "w") as f_out:
+    with open(os.devnull, "w") as f_out:
         exit_code = main(cmdline_args=args, stdin=io.StringIO(to_stdin), stdout=f_out)
 
     assert exit_code in {0, 3, 4}

tests/test_real_projects.py

@@ -7,7 +7,9 @@
 """
 import json
 import logging
+import os
 import subprocess
+import sys
 import tarfile
 from dataclasses import dataclass
 from pathlib import Path
@@ -51,7 +53,7 @@ def verify_requirements(venv_path: Path, requirements: List[str]) -> None:
 def run_fawltydeps_json(
     *args: str, venv_dir: Optional[Path], cwd: Optional[Path] = None
 ) -> JsonData:
-    argv = ["fawltydeps", "--config-file=/dev/null", "--json"]
+    argv = [sys.executable, "-m", "fawltydeps", f"--config-file={os.devnull}", "--json"]
     if venv_dir is not None:
         argv += [f"--pyenv={venv_dir}"]
     proc = subprocess.run(

tests/utils.py

@@ -4,6 +4,7 @@
 import logging
 import os
 import subprocess
+import sys
 from dataclasses import dataclass, field, replace
 from pathlib import Path
 from pprint import pformat
@@ -106,13 +107,14 @@ def unused_factory(*deps: str) -> List[UnusedDependency]:
 
 def run_fawltydeps_subprocess(
     *args: str,
-    config_file: Path = Path("/dev/null"),
+    config_file: Path = Path(os.devnull),
     to_stdin: Optional[str] = None,
     cwd: Optional[Path] = None,
 ) -> Tuple[str, str, int]:
     """Run FawltyDeps as a subprocess. Designed for integration tests."""
     proc = subprocess.run(
-        ["fawltydeps", f"--config-file={config_file}"] + list(args),
+        [sys.executable, "-m", "fawltydeps", f"--config-file={config_file}"]
+        + list(args),
         input=to_stdin,
         stdout=subprocess.PIPE,
         stderr=subprocess.PIPE,
@@ -131,7 +133,7 @@ def run_fawltydeps_subprocess(
 
 def run_fawltydeps_function(
     *args: str,
-    config_file: Path = Path("/dev/null"),
+    config_file: Path = Path(os.devnull),
     to_stdin: Optional[Union[str, bytes]] = None,
     basepath: Optional[Path] = None,
 ) -> Tuple[str, int]: