Fix failures with long Python interpreter paths

When `sys.executable` is long, it may exceed the kernel limits for shebangs, which results in `OSError: [Errno 8] Exec format error: 'foo'` when launching a tool injected into `PATH.

This is fixed by symlinking the Python interpreter to a short path and emitting that into the shebang.

testpath/commands.py

@@ -74,8 +74,12 @@ def __init__(self, name, content=None, python=''):
         self.command_dir = tempfile.mkdtemp()
 
         if content is None:
+            # Shebangs have a limited length, so symlink the Python executable
+            # to a short name that can't conflict with the real command.
+            tmp_python = os.path.join(self.command_dir, 'python-' + name)
+            os.symlink(sys.executable, tmp_python)
             content = _record_run.format(
-                python=sys.executable, recording_file=self.recording_file,
+                python=tmp_python, recording_file=self.recording_file,
                 extra_code=python,
             )
         elif python:

tests/test_commands.py

@@ -1,6 +1,9 @@
 import os
 from subprocess import call, check_output
 import unittest
+import shutil
+import sys
+import tempfile
 
 from testpath.commands import *
 
@@ -35,6 +38,26 @@ def test_assert_calls_twice(self):
             with assert_calls('git'):
                 pass
 
+    def test_assert_calls_long_python_path(self):
+        current_python = sys.executable
+        tmp = tempfile.mkdtemp()
+        try:
+            tmp_python_dir = tmp
+            for _ in range(10):
+                tmp_python_dir = os.path.join(tmp_python_dir, 'looooooooooooooooooooooooooooooooooooooooooong_segment')
+            os.makedirs(tmp_python_dir)
+            tmp_python = os.path.join(tmp_python_dir, 'python')
+            os.symlink(sys.executable, tmp_python)
+            sys.executable = tmp_python
+
+            with assert_calls('i_dont_exist'):
+                call(['i_dont_exist'])
+            with assert_calls('git'):
+                call(['git'])
+        finally:
+            sys.executable = current_python
+            shutil.rmtree(tmp, ignore_errors=True)
+
 def test_fixed_output():
     t = 'Sat 24 Apr 17:11:58 BST 2021\n'
     with MockCommand.fixed_output('date', t) as mock_date: