pytest mock for external HTTP API calls

<p>My application makes calls to the OpenAI API and other external services. I want to write unit tests that don't make real HTTP calls, can test different response scenarios (success, error, timeout), and don't require API keys in CI.</p>

<p>Use <code>pytest-httpx</code> or <code>respx</code> to mock httpx calls:</p> <div class="highlight"><pre><span></span><code><span class="c1"># pip install respx pytest-httpx</span> <span class="kn">import</span><span class="w"> </span><span class="nn">pytest</span> <span class="kn">from</span><span class="w"> </span><span class="nn">unittest.mock</span><span class="w"> </span><span class="kn">import</span> <span class="n">AsyncMock</span><span class="p">,</span> <span class="n">patch</span> <span class="c1"># Option 1: respx for httpx mocking</span> <span class="kn">import</span><span class="w"> </span><span class="nn">respx</span> <span class="kn">import</span><span class="w"> </span><span class="nn">httpx</span> <span class="nd">@pytest</span><span class="o">.</span><span class="n">mark</span><span class="o">.</span><span class="n">asyncio</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">test_embedding_success</span><span class="p">():</span> <span class="n">mock_response</span> <span class="o">=</span> <span class="p">{</span><span class="s1">'data'</span><span class="p">:</span> <span class="p">[{</span><span class="s1">'embedding'</span><span class="p">:</span> <span class="p">[</span><span class="mf">0.1</span><span class="p">]</span> <span class="o">*</span> <span class="mi">1536</span><span class="p">}],</span> <span class="s1">'usage'</span><span class="p">:</span> <span class="p">{</span><span class="s1">'total_tokens'</span><span class="p">:</span> <span class="mi">10</span><span class="p">}}</span> <span class="k">with</span> <span class="n">respx</span><span class="o">.</span><span class="n">mock</span><span class="p">:</span> <span class="n">respx</span><span class="o">.</span><span class="n">post</span><span class="p">(</span><span class="s1">'https://api.openai.com/v1/embeddings'</span><span class="p">)</span><span class="o">.</span><span class="n">mock</span><span class="p">(</span> <span class="n">return_value</span><span class="o">=</span><span class="n">httpx</span><span class="o">.</span><span class="n">Response</span><span class="p">(</span><span class="mi">200</span><span class="p">,</span> <span class="n">json</span><span class="o">=</span><span class="n">mock_response</span><span class="p">)</span> <span class="p">)</span> <span class="n">result</span> <span class="o">=</span> <span class="k">await</span> <span class="n">generate_embedding</span><span class="p">(</span><span class="s1">'test text'</span><span class="p">)</span> <span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">result</span><span class="p">)</span> <span class="o">==</span> <span class="mi">1536</span> <span class="nd">@pytest</span><span class="o">.</span><span class="n">mark</span><span class="o">.</span><span class="n">asyncio</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">test_embedding_timeout</span><span class="p">():</span> <span class="k">with</span> <span class="n">respx</span><span class="o">.</span><span class="n">mock</span><span class="p">:</span> <span class="n">respx</span><span class="o">.</span><span class="n">post</span><span class="p">(</span><span class="s1">'https://api.openai.com/v1/embeddings'</span><span class="p">)</span><span class="o">.</span><span class="n">mock</span><span class="p">(</span> <span class="n">side_effect</span><span class="o">=</span><span class="n">httpx</span><span class="o">.</span><span class="n">TimeoutException</span><span class="p">(</span><span class="s1">'Timeout'</span><span class="p">)</span> <span class="p">)</span> <span class="n">result</span> <span class="o">=</span> <span class="k">await</span> <span class="n">generate_embedding</span><span class="p">(</span><span class="s1">'test text'</span><span class="p">)</span> <span class="k">assert</span> <span class="n">result</span> <span class="ow">is</span> <span class="kc">None</span> <span class="c1"># Should fail gracefully</span> <span class="c1"># Option 2: patch for simple cases</span> <span class="nd">@pytest</span><span class="o">.</span><span class="n">mark</span><span class="o">.</span><span class="n">asyncio</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">test_with_patch</span><span class="p">():</span> <span class="k">with</span> <span class="n">patch</span><span class="p">(</span><span class="s1">'app.services.embeddings.openai_client.embeddings.create'</span><span class="p">)</span> <span class="k">as</span> <span class="n">mock_create</span><span class="p">:</span> <span class="n">mock_create</span><span class="o">.</span><span class="n">return_value</span> <span class="o">=</span> <span class="n">AsyncMock</span><span class="p">(</span> <span class="n">data</span><span class="o">=</span><span class="p">[</span><span class="n">AsyncMock</span><span class="p">(</span><span class="n">embedding</span><span class="o">=</span><span class="p">[</span><span class="mf">0.1</span><span class="p">]</span> <span class="o">*</span> <span class="mi">1536</span><span class="p">)]</span> <span class="p">)</span> <span class="n">result</span> <span class="o">=</span> <span class="k">await</span> <span class="n">generate_embedding</span><span class="p">(</span><span class="s1">'test'</span><span class="p">)</span> <span class="k">assert</span> <span class="n">result</span> <span class="ow">is</span> <span class="ow">not</span> <span class="kc">None</span> </code></pre></div> <p>Key points: - <code>respx</code> integrates with httpx at the transport level — no real HTTP requests - Test both success and failure paths — timeouts, 429s, 500s - <code>AsyncMock</code> is required for async functions in <code>unittest.mock</code> - Use <code>pytest.fixture</code> to share mock setups across multiple tests</p>