Fix JsException passing from pyodide environment to host

pytest_pyodide/decorator.py

@@ -4,11 +4,13 @@
 from base64 import b64decode, b64encode
 from collections.abc import Callable, Collection
 from copy import deepcopy
+from io import BytesIO
 from typing import Any
 
 import pytest
 
 from .hook import ORIGINAL_MODULE_ASTS, REWRITTEN_MODULE_ASTS
+from .pyodide import JsException
 from .utils import package_is_built as _package_is_built
 
 
@@ -35,6 +37,25 @@ def _encode(obj: Any) -> str:
     return b64encode(pickle.dumps(obj)).decode()
 
 
+class Unpickler(pickle.Unpickler):
+    def find_class(self, module, name):
+        """
+        Catch exceptions that only exist in the pyodide environment and
+        convert them to exception in the host.
+        """
+        if module == "pyodide" and name == "JsException":
+            return JsException
+        else:
+            return super().find_class(module, name)
+
+
+def _decode(result: str) -> Any:
+    buffer = BytesIO()
+    buffer.write(b64decode(result))
+    buffer.seek(0)
+    return Unpickler(buffer).load()
+
+
 def _create_outer_test_function(
     run_test: Callable,
     node: Any,
@@ -229,7 +250,7 @@ def _run_test(self, selenium: SeleniumType, args: tuple):
         r = selenium.run_async(code)
         [status, result] = r
 
-        result = pickle.loads(b64decode(result))
+        result = _decode(result)
         if status:
             raise result
         else:

pytest_pyodide/pyodide.py

@@ -0,0 +1,15 @@
+class JsException(Exception):
+    """
+    The python code of the test can call javascript functions using
+    ```
+    from js import XMLHttpRequest
+
+    xhr = XMLHttpRequest.new()
+    xhr.responseType = 'arraybuffer';
+    xhr.open('url', None, False)  # this will fail in main thread
+    ```
+
+    The code fails and raises a `JsException` in the pyodide environment. When the exception
+    is sent back to host, the host tries to unpickle the exception. The unpickle will fail
+    because "pyodide.JsException" only exists in the pyodide environment.
+    """

tests/test_decorator.py

@@ -3,6 +3,7 @@
 
 from pytest_pyodide.decorator import run_in_pyodide
 from pytest_pyodide.hypothesis import any_strategy, std_hypothesis_settings
+from pytest_pyodide.pyodide import JsException
 from pytest_pyodide.utils import parse_driver_timeout
 
 
@@ -69,6 +70,20 @@ def inner_function(selenium, x):
     assert inner_function(selenium, 6) == 7
 
 
+def test_inner_function_js_exception(selenium):
+    @run_in_pyodide
+    def inner_function(selenium):
+        from js import eval as js_eval
+
+        js_eval("throw 'some error'")
+
+    with pytest.raises(
+        JsException,
+        match="Error: some error",
+    ):
+        inner_function(selenium)
+
+
 def complicated_decorator(attr_name: str):
     def inner_func(value):
         def dec(func):