run_tests: turn into multicall program

Add shortcuts to easily run individual tools while re-using the embedded
vpython/UV script settings.

Change-Id: I4c63e7fd402666628a18cc77187c958d93910f80
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/656245
Tested-by: Mike Frysinger <vapier@google.com>
Commit-Queue: Mike Frysinger <vapier@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

black

@@ -0,0 +1 @@
+run_tests

flake8

@@ -0,0 +1 @@
+run_tests

isort

@@ -0,0 +1 @@
+run_tests

pytest

@@ -0,0 +1 @@
+run_tests

run_tests

@@ -34,10 +34,14 @@
 import functools
 import os
 import shlex
-import shutil
 import subprocess
 import sys
 
+import black
+import flake8.main.cli
+import isort.main
+import pytest
+
 
 # NB: While tests/* support Python >=3.6 to match requirements.json for `repo`,
 # the higher level runner logic does not need to be held back.
@@ -202,8 +206,8 @@ def cipd_bootstrap() -> None:
         return
 
 
-def main(argv):
-    """The main entry."""
+def main_run_tests(argv: list[str]) -> int:
+    """The run_tests program."""
     cipd_bootstrap()
     checks = (
         functools.partial(run_pytest, argv),
@@ -219,5 +223,21 @@ def main(argv):
     return 1 if sum(c() for c in checks) else 0
 
 
+main_black = black.main
+main_flake8 = flake8.main.cli.main
+main_isort = isort.main.main
+main_pytest = pytest.main
+
+
+def main(argv: list[str]) -> int:
+    """The main dispatcher."""
+    # Figure out what script we're running as and dispatch to its main.
+    # This makes it easier for people to use the same env as run_tests.
+    argv0 = os.path.basename(sys.argv[0])
+    funcname = f"main_{argv0}"
+    func = globals().get(funcname, main_run_tests)
+    return func(argv)
+
+
 if __name__ == "__main__":
     sys.exit(main(sys.argv[1:]))