test: adding 21 tests for client/card_resolver.py (#592)

# Description

Adding 21 tests for client/card_resolver.py

They all pass:

```
========================= test session starts ==============================
collecting ... collected 21 items

tests/client/test_card_resolver.py::TestA2ACardResolverInit::test_init_with_defaults PASSED [  4%]
tests/client/test_card_resolver.py::TestA2ACardResolverInit::test_init_with_custom_path PASSED [  9%]
tests/client/test_card_resolver.py::TestA2ACardResolverInit::test_init_strips_leading_slash_from_agent_card_path PASSED [ 14%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_success_default_path PASSED [ 19%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_success_custom_path PASSED [ 23%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_strips_leading_slash_from_relative_path PASSED [ 28%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_with_http_kwargs PASSED [ 33%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_root_path PASSED [ 38%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_http_status_error PASSED [ 42%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_json_decode_error PASSED [ 47%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_request_error PASSED [ 52%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_validation_error PASSED [ 57%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_logs_success PASSED [ 61%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_none_relative_path PASSED [ 66%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_empty_string_relative_path PASSED [ 71%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_different_status_codes[400] PASSED [ 76%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_different_status_codes[401] PASSED [ 80%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_different_status_codes[403] PASSED [ 85%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_different_status_codes[500] PASSED [ 90%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_different_status_codes[502] PASSED [ 95%]
tests/client/test_card_resolver.py::TestGetAgentCard::test_get_agent_card_returns_agent_card_instance PASSED [100%]

======================== 21 passed, 2 warnings in 0.11s ========================
```

- [X] Follow the [`CONTRIBUTING`
Guide](https://github.com/a2aproject/a2a-python/blob/main/CONTRIBUTING.md).
- [X] Make your Pull Request title in the
<https://www.conventionalcommits.org/> specification.
- [X] Ensure the tests and linter pass (Run `bash scripts/format.sh`
from the repository root to format)
- [N/A ] Appropriate docs were updated (if necessary)

Fixes #<issue_number_goes_here> 🦕

N/A

---------

Co-authored-by: Lukasz Kawka <luk.kawka@gmail.com>

Author: didier-durand

tests/client/test_card_resolver.py

@@ -0,0 +1,379 @@
+import json
+import logging
+
+from unittest.mock import AsyncMock, Mock, patch
+
+import httpx
+import pytest
+
+from a2a.client import A2ACardResolver, A2AClientHTTPError, A2AClientJSONError
+from a2a.types import AgentCard
+from a2a.utils import AGENT_CARD_WELL_KNOWN_PATH
+
+
+@pytest.fixture
+def mock_httpx_client():
+    """Fixture providing a mocked async httpx client."""
+    return AsyncMock(spec=httpx.AsyncClient)
+
+
+@pytest.fixture
+def base_url():
+    """Fixture providing a test base URL."""
+    return 'https://example.com'
+
+
+@pytest.fixture
+def resolver(mock_httpx_client, base_url):
+    """Fixture providing an A2ACardResolver instance."""
+    return A2ACardResolver(
+        httpx_client=mock_httpx_client,
+        base_url=base_url,
+    )
+
+
+@pytest.fixture
+def mock_response():
+    """Fixture providing a mock httpx Response."""
+    response = Mock(spec=httpx.Response)
+    response.raise_for_status = Mock()
+    return response
+
+
+@pytest.fixture
+def valid_agent_card_data():
+    """Fixture providing valid agent card data."""
+    return {
+        'name': 'TestAgent',
+        'description': 'A test agent',
+        'version': '1.0.0',
+        'url': 'https://example.com/a2a',
+        'capabilities': {},
+        'default_input_modes': ['text/plain'],
+        'default_output_modes': ['text/plain'],
+        'skills': [
+            {
+                'id': 'test-skill',
+                'name': 'Test Skill',
+                'description': 'A skill for testing',
+                'tags': ['test'],
+            }
+        ],
+    }
+
+
+class TestA2ACardResolverInit:
+    """Tests for A2ACardResolver initialization."""
+
+    def test_init_with_defaults(self, mock_httpx_client, base_url):
+        """Test initialization with default agent_card_path."""
+        resolver = A2ACardResolver(
+            httpx_client=mock_httpx_client,
+            base_url=base_url,
+        )
+        assert resolver.base_url == base_url
+        assert resolver.agent_card_path == AGENT_CARD_WELL_KNOWN_PATH[1:]
+        assert resolver.httpx_client == mock_httpx_client
+
+    def test_init_with_custom_path(self, mock_httpx_client, base_url):
+        """Test initialization with custom agent_card_path."""
+        custom_path = '/custom/agent/card'
+        resolver = A2ACardResolver(
+            httpx_client=mock_httpx_client,
+            base_url=base_url,
+            agent_card_path=custom_path,
+        )
+        assert resolver.base_url == base_url
+        assert resolver.agent_card_path == custom_path[1:]
+
+    def test_init_strips_leading_slash_from_agent_card_path(
+        self, mock_httpx_client, base_url
+    ):
+        """Test that leading slash is stripped from agent_card_path."""
+        agent_card_path = '/well-known/agent'
+        resolver = A2ACardResolver(
+            httpx_client=mock_httpx_client,
+            base_url=base_url,
+            agent_card_path=agent_card_path,
+        )
+        assert resolver.agent_card_path == agent_card_path[1:]
+
+
+class TestGetAgentCard:
+    """Tests for get_agent_card methods."""
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_success_default_path(
+        self,
+        base_url,
+        resolver,
+        mock_httpx_client,
+        mock_response,
+        valid_agent_card_data,
+    ):
+        """Test successful agent card fetch using default path."""
+        mock_response.json.return_value = valid_agent_card_data
+        mock_httpx_client.get.return_value = mock_response
+
+        with patch.object(
+            AgentCard, 'model_validate', return_value=Mock(spec=AgentCard)
+        ) as mock_validate:
+            result = await resolver.get_agent_card()
+            mock_httpx_client.get.assert_called_once_with(
+                f'{base_url}/{AGENT_CARD_WELL_KNOWN_PATH[1:]}',
+            )
+            mock_response.raise_for_status.assert_called_once()
+            mock_response.json.assert_called_once()
+            mock_validate.assert_called_once_with(valid_agent_card_data)
+            assert result is not None
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_success_custom_path(
+        self,
+        base_url,
+        resolver,
+        mock_httpx_client,
+        mock_response,
+        valid_agent_card_data,
+    ):
+        """Test successful agent card fetch using custom relative path."""
+        custom_path = 'custom/path/card'
+        mock_response.json.return_value = valid_agent_card_data
+        mock_httpx_client.get.return_value = mock_response
+        with patch.object(
+            AgentCard, 'model_validate', return_value=Mock(spec=AgentCard)
+        ):
+            await resolver.get_agent_card(relative_card_path=custom_path)
+
+            mock_httpx_client.get.assert_called_once_with(
+                f'{base_url}/{custom_path}',
+            )
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_strips_leading_slash_from_relative_path(
+        self,
+        base_url,
+        resolver,
+        mock_httpx_client,
+        mock_response,
+        valid_agent_card_data,
+    ):
+        """Test successful agent card fetch using custom path with leading slash."""
+        custom_path = '/custom/path/card'
+        mock_response.json.return_value = valid_agent_card_data
+        mock_httpx_client.get.return_value = mock_response
+        with patch.object(
+            AgentCard, 'model_validate', return_value=Mock(spec=AgentCard)
+        ):
+            await resolver.get_agent_card(relative_card_path=custom_path)
+
+            mock_httpx_client.get.assert_called_once_with(
+                f'{base_url}/{custom_path[1:]}',
+            )
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_with_http_kwargs(
+        self,
+        base_url,
+        resolver,
+        mock_httpx_client,
+        mock_response,
+        valid_agent_card_data,
+    ):
+        """Test that http_kwargs are passed to httpx.get."""
+        mock_response.json.return_value = valid_agent_card_data
+        mock_httpx_client.get.return_value = mock_response
+        http_kwargs = {
+            'timeout': 30,
+            'headers': {'Authorization': 'Bearer token'},
+        }
+        with patch.object(
+            AgentCard, 'model_validate', return_value=Mock(spec=AgentCard)
+        ):
+            await resolver.get_agent_card(http_kwargs=http_kwargs)
+            mock_httpx_client.get.assert_called_once_with(
+                f'{base_url}/{AGENT_CARD_WELL_KNOWN_PATH[1:]}',
+                timeout=30,
+                headers={'Authorization': 'Bearer token'},
+            )
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_root_path(
+        self,
+        base_url,
+        resolver,
+        mock_httpx_client,
+        mock_response,
+        valid_agent_card_data,
+    ):
+        """Test fetching agent card from root path."""
+        mock_response.json.return_value = valid_agent_card_data
+        mock_httpx_client.get.return_value = mock_response
+        with patch.object(
+            AgentCard, 'model_validate', return_value=Mock(spec=AgentCard)
+        ):
+            await resolver.get_agent_card(relative_card_path='/')
+            mock_httpx_client.get.assert_called_once_with(f'{base_url}/')
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_http_status_error(
+        self, resolver, mock_httpx_client
+    ):
+        """Test A2AClientHTTPError raised on HTTP status error."""
+        status_code = 404
+        mock_response = Mock(spec=httpx.Response)
+        mock_response.status_code = status_code
+        mock_response.raise_for_status.side_effect = httpx.HTTPStatusError(
+            'Not Found', request=Mock(), response=mock_response
+        )
+        mock_httpx_client.get.return_value = mock_response
+
+        with pytest.raises(A2AClientHTTPError) as exc_info:
+            await resolver.get_agent_card()
+
+        assert exc_info.value.status_code == status_code
+        assert 'Failed to fetch agent card' in str(exc_info.value)
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_json_decode_error(
+        self, resolver, mock_httpx_client, mock_response
+    ):
+        """Test A2AClientJSONError raised on JSON decode error."""
+        mock_response.json.side_effect = json.JSONDecodeError(
+            'Invalid JSON', '', 0
+        )
+        mock_httpx_client.get.return_value = mock_response
+        with pytest.raises(A2AClientJSONError) as exc_info:
+            await resolver.get_agent_card()
+        assert 'Failed to parse JSON' in str(exc_info.value)
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_request_error(
+        self, resolver, mock_httpx_client
+    ):
+        """Test A2AClientHTTPError raised on network request error."""
+        mock_httpx_client.get.side_effect = httpx.RequestError(
+            'Connection timeout', request=Mock()
+        )
+        with pytest.raises(A2AClientHTTPError) as exc_info:
+            await resolver.get_agent_card()
+        assert exc_info.value.status_code == 503
+        assert 'Network communication error' in str(exc_info.value)
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_validation_error(
+        self,
+        base_url,
+        resolver,
+        mock_httpx_client,
+        mock_response,
+        valid_agent_card_data,
+    ):
+        """Test A2AClientJSONError is raised on agent card validation error."""
+        return_json = {'invalid': 'data'}
+        mock_response.json.return_value = return_json
+        mock_httpx_client.get.return_value = mock_response
+        with pytest.raises(A2AClientJSONError) as exc_info:
+            await resolver.get_agent_card()
+        assert (
+            f'Failed to validate agent card structure from {base_url}/{AGENT_CARD_WELL_KNOWN_PATH[1:]}'
+            in exc_info.value.message
+        )
+        mock_httpx_client.get.assert_called_once_with(
+            f'{base_url}/{AGENT_CARD_WELL_KNOWN_PATH[1:]}',
+        )
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_logs_success(  # noqa: PLR0913
+        self,
+        base_url,
+        resolver,
+        mock_httpx_client,
+        mock_response,
+        valid_agent_card_data,
+        caplog,
+    ):
+        mock_response.json.return_value = valid_agent_card_data
+        mock_httpx_client.get.return_value = mock_response
+        with (
+            patch.object(
+                AgentCard, 'model_validate', return_value=Mock(spec=AgentCard)
+            ),
+            caplog.at_level(logging.INFO),
+        ):
+            await resolver.get_agent_card()
+        assert (
+            f'Successfully fetched agent card data from {base_url}/{AGENT_CARD_WELL_KNOWN_PATH[1:]}'
+            in caplog.text
+        )
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_none_relative_path(
+        self,
+        base_url,
+        resolver,
+        mock_httpx_client,
+        mock_response,
+        valid_agent_card_data,
+    ):
+        """Test that None relative_card_path uses default path."""
+        mock_response.json.return_value = valid_agent_card_data
+        mock_httpx_client.get.return_value = mock_response
+
+        with patch.object(
+            AgentCard, 'model_validate', return_value=Mock(spec=AgentCard)
+        ):
+            await resolver.get_agent_card(relative_card_path=None)
+            mock_httpx_client.get.assert_called_once_with(
+                f'{base_url}/{AGENT_CARD_WELL_KNOWN_PATH[1:]}',
+            )
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_empty_string_relative_path(
+        self,
+        base_url,
+        resolver,
+        mock_httpx_client,
+        mock_response,
+        valid_agent_card_data,
+    ):
+        """Test that empty string relative_card_path uses default path."""
+        mock_response.json.return_value = valid_agent_card_data
+        mock_httpx_client.get.return_value = mock_response
+
+        with patch.object(
+            AgentCard, 'model_validate', return_value=Mock(spec=AgentCard)
+        ):
+            await resolver.get_agent_card(relative_card_path='')
+
+            mock_httpx_client.get.assert_called_once_with(
+                f'{base_url}/{AGENT_CARD_WELL_KNOWN_PATH[1:]}',
+            )
+
+    @pytest.mark.parametrize('status_code', [400, 401, 403, 500, 502])
+    @pytest.mark.asyncio
+    async def test_get_agent_card_different_status_codes(
+        self, resolver, mock_httpx_client, status_code
+    ):
+        """Test different HTTP status codes raise appropriate errors."""
+        mock_response = Mock(spec=httpx.Response)
+        mock_response.status_code = status_code
+        mock_response.raise_for_status.side_effect = httpx.HTTPStatusError(
+            f'Status {status_code}', request=Mock(), response=mock_response
+        )
+        mock_httpx_client.get.return_value = mock_response
+        with pytest.raises(A2AClientHTTPError) as exc_info:
+            await resolver.get_agent_card()
+        assert exc_info.value.status_code == status_code
+
+    @pytest.mark.asyncio
+    async def test_get_agent_card_returns_agent_card_instance(
+        self, resolver, mock_httpx_client, mock_response, valid_agent_card_data
+    ):
+        """Test that get_agent_card returns an AgentCard instance."""
+        mock_agent_card = Mock(spec=AgentCard)
+        with patch.object(
+            AgentCard, 'model_validate', return_value=mock_agent_card
+        ):
+            result = await resolver.get_agent_card()
+            assert result == mock_agent_card