activate.fish: update fish major version check

src/virtualenv/activation/fish/activate.fish

@@ -18,7 +18,7 @@ function deactivate -d 'Exit virtualenv mode and return to the normal environmen
     # reset old environment variables
     if test -n "$_OLD_VIRTUAL_PATH"
         # https://github.com/fish-shell/fish-shell/issues/436 altered PATH handling
-        if test (echo $FISH_VERSION | head -c 1) -lt 3
+        if test (string sub -s 1 -l 1 $FISH_VERSION) -lt 3
             set -gx PATH (_fishify_path "$_OLD_VIRTUAL_PATH")
         else
             set -gx PATH $_OLD_VIRTUAL_PATH
@@ -61,7 +61,7 @@ deactivate nondestructive
 set -gx VIRTUAL_ENV __VIRTUAL_ENV__
 
 # https://github.com/fish-shell/fish-shell/issues/436 altered PATH handling
-if test (echo $FISH_VERSION | head -c 1) -lt 3
+if test (string sub -s 1 -l 1 $FISH_VERSION) -lt 3
     set -gx _OLD_VIRTUAL_PATH (_bashify_path $PATH)
 else
     set -gx _OLD_VIRTUAL_PATH $PATH

tests/unit/activation/test_fish.py

@@ -1,5 +1,8 @@
 from __future__ import annotations
 
+import os
+import sys
+
 import pytest
 
 from virtualenv.activation import FishActivator
@@ -20,4 +23,54 @@ def __init__(self, session) -> None:
         def print_prompt(self):
             return "fish_prompt"
 
+        def _get_test_lines(self, activate_script):
+            return [
+                self.print_python_exe(),
+                self.print_os_env_var("VIRTUAL_ENV"),
+                self.print_os_env_var("VIRTUAL_ENV_PROMPT"),
+                self.print_os_env_var("PATH"),
+                self.activate_call(activate_script),
+                self.print_python_exe(),
+                self.print_os_env_var("VIRTUAL_ENV"),
+                self.print_os_env_var("VIRTUAL_ENV_PROMPT"),
+                self.print_os_env_var("PATH"),
+                self.print_prompt(),
+                # \\ loads documentation from the virtualenv site packages
+                self.pydoc_call,
+                self.deactivate,
+                self.print_python_exe(),
+                self.print_os_env_var("VIRTUAL_ENV"),
+                self.print_os_env_var("VIRTUAL_ENV_PROMPT"),
+                self.print_os_env_var("PATH"),
+                "",  # just finish with an empty new line
+            ]
+
+        def assert_output(self, out, raw, _):
+            # pre-activation
+            assert out[0], raw
+            assert out[1] == "None", raw
+            assert out[2] == "None", raw
+            # post-activation
+            expected = self._creator.exe.parent / os.path.basename(sys.executable)
+            assert self.norm_path(out[4]) == self.norm_path(expected), raw
+            assert self.norm_path(out[5]) == self.norm_path(self._creator.dest).replace("\\\\", "\\"), raw
+            assert out[6] == self._creator.env_name
+            # Some attempts to test the prompt output print more than 1 line.
+            # So we need to check if the prompt exists on any of them.
+            prompt_text = f"({self._creator.env_name}) "
+            assert any(prompt_text in line for line in out[7:-5]), raw
+
+            assert out[-5] == "wrote pydoc_test.html", raw
+            content = tmp_path / "pydoc_test.html"
+            assert content.exists(), raw
+            # post deactivation, same as before
+            assert out[-4] == out[0], raw
+            assert out[-3] == "None", raw
+            assert out[-2] == "None", raw
+
+            # Check that the PATH is restored
+            assert out[3] == out[13], raw
+            # Check that PATH changed after activation
+            assert out[3] != out[8], raw
+
     activation_tester(Fish)