diff --git a/test/unit/webdriver/errorhandler_test.py b/test/unit/webdriver/errorhandler_test.py
new file mode 100644
index 00000000..6f10e4a0
--- /dev/null
+++ b/test/unit/webdriver/errorhandler_test.py
@@ -0,0 +1,177 @@
+#!/usr/bin/env python
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import json
+
+import pytest
+import selenium.common.exceptions as sel_exceptions
+
+import appium.common.exceptions as appium_exceptions
+from appium.webdriver.errorhandler import MobileErrorHandler, format_stacktrace
+
+
+class TestFormatStacktrace:
+    def test_format_stacktrace_none_or_empty(self):
+        assert format_stacktrace(None) == []
+        assert format_stacktrace('') == []
+        assert format_stacktrace([]) == []
+
+    def test_format_stacktrace_string(self):
+        stacktrace_str = 'line1\nline2\nline3'
+        assert format_stacktrace(stacktrace_str) == ['line1', 'line2', 'line3']
+
+    def test_format_stacktrace_sequence_dicts(self):
+        stacktrace_seq = [
+            {
+                'lineNumber': 42,
+                'fileName': 'test.js',
+                'methodName': 'myMethod',
+                'className': 'MyClass',
+            },
+            {
+                'fileName': 'test2.js',
+                'methodName': 'topLevelFunc',
+            },
+            'not_a_dict',
+        ]
+        expected = [
+            '    at MyClass.myMethod (test.js:42)',
+            '    at topLevelFunc (test2.js)',
+        ]
+        assert format_stacktrace(stacktrace_seq) == expected
+
+    def test_format_stacktrace_type_error_exception(self):
+        class NonIterable:
+            def __iter__(self):
+                raise TypeError('Not iterable')
+
+        assert format_stacktrace(NonIterable()) == []
+
+
+class TestMobileErrorHandler:
+    def setup_method(self):
+        self.handler = MobileErrorHandler()
+
+    def test_check_response_valid_no_error(self):
+        # Empty response or response without error should return None without raising
+        self.handler.check_response({})
+        self.handler.check_response({'value': ''})
+        self.handler.check_response({'value': None})
+        self.handler.check_response({'value': {}})
+        self.handler.check_response({'value': {'value': {}}})
+        self.handler.check_response({'value': {'value': {'error': None}}})
+
+    def test_check_response_invalid_json_str_payload(self):
+        # Invalid JSON string in value payload should be caught and return None
+        self.handler.check_response({'value': 'invalid json {['})
+
+    def test_check_response_json_decode_error_and_type_error(self):
+        # Non-string/non-dict payload types (e.g. integer or list if not handled as dict)
+        self.handler.check_response({'value': 12345})
+
+    def test_check_response_json_payload_decodes_to_non_dict(self):
+        # Valid JSON string decoding to int or list (not a dict)
+        self.handler.check_response({'value': '123'})
+        self.handler.check_response({'value': '[1, 2, 3]'})
+
+    def test_check_response_payload_value_is_not_dict(self):
+        # Response with dict payload where payload.get('value') is not a dict
+        self.handler.check_response({'value': {'value': 'string_value'}})
+        self.handler.check_response({'value': '{"value": 123}'})
+
+    def test_check_response_mapped_selenium_error(self):
+        # Response triggering a mapped Selenium exception
+        response = {
+            'value': {
+                'value': {
+                    'error': 'no such element',
+                    'message': 'Element not found',
+                    'stacktrace': 'Traceback line 1\nTraceback line 2',
+                }
+            }
+        }
+        with pytest.raises(sel_exceptions.NoSuchElementException) as exc_info:
+            self.handler.check_response(response)
+        assert exc_info.value.msg is not None
+        assert 'Element not found' in exc_info.value.msg
+        assert exc_info.value.stacktrace == ['Traceback line 1', 'Traceback line 2']
+
+    def test_check_response_json_str_mapped_selenium_error(self):
+        # Payload as a JSON string
+        payload = json.dumps(
+            {
+                'value': {
+                    'error': 'stale element reference',
+                    'message': 'Element is stale',
+                }
+            }
+        )
+        with pytest.raises(sel_exceptions.StaleElementReferenceException) as exc_info:
+            self.handler.check_response({'value': payload})
+        assert exc_info.value.msg is not None
+        assert 'Element is stale' in exc_info.value.msg
+
+    def test_check_response_unmapped_error_defaults_to_webdriver_exception(self):
+        response = {
+            'value': {
+                'value': {
+                    'error': 'custom_unknown_error_code',
+                    'message': 'Something failed',
+                }
+            }
+        }
+        with pytest.raises(sel_exceptions.WebDriverException) as exc_info:
+            self.handler.check_response(response)
+        assert exc_info.value.msg == 'Something failed'
+
+    def test_check_response_no_such_context_exception(self):
+        response = {
+            'value': {
+                'value': {
+                    'error': 'unknown error',
+                    'message': 'No such context found.',
+                }
+            }
+        }
+        with pytest.raises(appium_exceptions.NoSuchContextException) as exc_info:
+            self.handler.check_response(response)
+        assert exc_info.value.msg == 'No such context found.'
+
+    def test_check_response_invalid_switch_to_target_exception(self):
+        response = {
+            'value': {
+                'value': {
+                    'error': 'unknown error',
+                    'message': 'That command could not be executed in the current context.',
+                }
+            }
+        }
+        with pytest.raises(appium_exceptions.InvalidSwitchToTargetException) as exc_info:
+            self.handler.check_response(response)
+        assert exc_info.value.msg == 'That command could not be executed in the current context.'
+
+    def test_check_response_unexpected_alert_present_exception(self):
+        response = {
+            'value': {
+                'value': {
+                    'error': 'unexpected alert open',
+                    'message': 'Alert present',
+                    'data': 'Alert text content',
+                }
+            }
+        }
+        with pytest.raises(sel_exceptions.UnexpectedAlertPresentException) as exc_info:
+            self.handler.check_response(response)
+        assert exc_info.value.msg == 'Alert present'
+        assert exc_info.value.alert_text == 'Alert text content'