Migrate the bin/dotbot script test to Python

tests/test_bin_dotbot.py

@@ -0,0 +1,55 @@
+import os
+import subprocess
+
+import pytest
+
+
+def which(name):
+    """Find an executable.
+
+    Python 2.7 doesn't have shutil.which().
+    """
+
+    for path in os.environ["PATH"].split(os.pathsep):
+        if os.path.isfile(os.path.join(path, name)):
+            return os.path.join(path, name)
+
+
+@pytest.mark.skipif(
+    "sys.platform[:5] == 'win32'",
+    reason="The hybrid sh/Python dotbot script doesn't run on Windows platforms",
+)
+@pytest.mark.parametrize("python_name", (None, "python", "python2", "python3"))
+def test_find_python_executable(python_name, home, dotfiles):
+    """Verify that the sh/Python hybrid dotbot executable can find Python."""
+
+    dotfiles.write_config([])
+    dotbot_executable = os.path.join(
+        os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "bin", "dotbot"
+    )
+
+    # Create a link to sh.
+    tmp_bin = os.path.join(home, "tmp_bin")
+    os.makedirs(tmp_bin)
+    sh_path = which("sh")
+    os.symlink(sh_path, os.path.join(tmp_bin, "sh"))
+
+    if python_name:
+        with open(os.path.join(tmp_bin, python_name), "w") as file:
+            file.write("#!" + tmp_bin + "/sh\n")
+            file.write("exit 0\n")
+        os.chmod(os.path.join(tmp_bin, python_name), 0o777)
+    env = dict(os.environ)
+    env["PATH"] = tmp_bin
+
+    if python_name:
+        subprocess.check_call(
+            [dotbot_executable, "-c", dotfiles.config_filename],
+            env=env,
+        )
+    else:
+        with pytest.raises(subprocess.CalledProcessError):
+            subprocess.check_call(
+                [dotbot_executable, "-c", dotfiles.config_filename],
+                env=env,
+            )