pytest parametrize for testing multiple input cases

<p>I have a function that handles multiple edge cases and I want to test all of them without writing a separate test function per case. I want to use pytest's parametrize decorator to test with different inputs and expected outputs, including error cases.</p>

<p>Use <code>@pytest.mark.parametrize</code> for data-driven tests:</p> <div class="highlight"><pre><span></span><code><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">app.services.tags</span><span class="w"> </span><span class="kn">import</span> <span class="n">normalize_tag</span><span class="p">,</span> <span class="n">validate_tag</span> <span class="nd">@pytest</span><span class="o">.</span><span class="n">mark</span><span class="o">.</span><span class="n">parametrize</span><span class="p">(</span><span class="s1">'raw,expected'</span><span class="p">,</span> <span class="p">[</span> <span class="p">(</span><span class="s1">'Python'</span><span class="p">,</span> <span class="s1">'python'</span><span class="p">),</span> <span class="p">(</span><span class="s1">' React '</span><span class="p">,</span> <span class="s1">'react'</span><span class="p">),</span> <span class="p">(</span><span class="s1">'Node.js'</span><span class="p">,</span> <span class="s1">'node.js'</span><span class="p">),</span> <span class="p">(</span><span class="s1">'type-script'</span><span class="p">,</span> <span class="s1">'type-script'</span><span class="p">),</span> <span class="p">(</span><span class="s1">'A'</span> <span class="o">*</span> <span class="mi">60</span><span class="p">,</span> <span class="s1">'a'</span> <span class="o">*</span> <span class="mi">50</span><span class="p">),</span> <span class="c1"># truncated to 50</span> <span class="p">])</span> <span class="k">def</span><span class="w"> </span><span class="nf">test_normalize_tag</span><span class="p">(</span><span class="n">raw</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">expected</span><span class="p">:</span> <span class="nb">str</span><span class="p">):</span> <span class="k">assert</span> <span class="n">normalize_tag</span><span class="p">(</span><span class="n">raw</span><span class="p">)</span> <span class="o">==</span> <span class="n">expected</span> <span class="nd">@pytest</span><span class="o">.</span><span class="n">mark</span><span class="o">.</span><span class="n">parametrize</span><span class="p">(</span><span class="s1">'tag,valid'</span><span class="p">,</span> <span class="p">[</span> <span class="p">(</span><span class="s1">'python'</span><span class="p">,</span> <span class="kc">True</span><span class="p">),</span> <span class="p">(</span><span class="s1">'node.js'</span><span class="p">,</span> <span class="kc">True</span><span class="p">),</span> <span class="p">(</span><span class="s1">'my-tag'</span><span class="p">,</span> <span class="kc">True</span><span class="p">),</span> <span class="p">(</span><span class="s1">''</span><span class="p">,</span> <span class="kc">False</span><span class="p">),</span> <span class="p">(</span><span class="s1">'has space'</span><span class="p">,</span> <span class="kc">False</span><span class="p">),</span> <span class="p">(</span><span class="s1">'hello!'</span><span class="p">,</span> <span class="kc">False</span><span class="p">),</span> <span class="p">])</span> <span class="k">def</span><span class="w"> </span><span class="nf">test_validate_tag</span><span class="p">(</span><span class="n">tag</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">valid</span><span class="p">:</span> <span class="nb">bool</span><span class="p">):</span> <span class="k">assert</span> <span class="n">validate_tag</span><span class="p">(</span><span class="n">tag</span><span class="p">)</span> <span class="o">==</span> <span class="n">valid</span> <span class="c1"># Testing exceptions:</span> <span class="nd">@pytest</span><span class="o">.</span><span class="n">mark</span><span class="o">.</span><span class="n">parametrize</span><span class="p">(</span><span class="s1">'input,exc_type,match'</span><span class="p">,</span> <span class="p">[</span> <span class="p">(</span><span class="s1">''</span><span class="p">,</span> <span class="ne">ValueError</span><span class="p">,</span> <span class="s1">'empty'</span><span class="p">),</span> <span class="p">(</span><span class="kc">None</span><span class="p">,</span> <span class="ne">TypeError</span><span class="p">,</span> <span class="s1">'string'</span><span class="p">),</span> <span class="p">])</span> <span class="k">def</span><span class="w"> </span><span class="nf">test_errors</span><span class="p">(</span><span class="nb">input</span><span class="p">,</span> <span class="n">exc_type</span><span class="p">,</span> <span class="n">match</span><span class="p">):</span> <span class="k">with</span> <span class="n">pytest</span><span class="o">.</span><span class="n">raises</span><span class="p">(</span><span class="n">exc_type</span><span class="p">,</span> <span class="n">match</span><span class="o">=</span><span class="n">match</span><span class="p">):</span> <span class="n">process_input</span><span class="p">(</span><span class="nb">input</span><span class="p">)</span> <span class="c1"># IDs for readable output:</span> <span class="nd">@pytest</span><span class="o">.</span><span class="n">mark</span><span class="o">.</span><span class="n">parametrize</span><span class="p">(</span><span class="s1">'n'</span><span class="p">,</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">100</span><span class="p">],</span> <span class="n">ids</span><span class="o">=</span><span class="p">[</span><span class="s1">'zero'</span><span class="p">,</span> <span class="s1">'one'</span><span class="p">,</span> <span class="s1">'hundred'</span><span class="p">])</span> <span class="k">def</span><span class="w"> </span><span class="nf">test_count</span><span class="p">(</span><span class="n">n</span><span class="p">):</span> <span class="k">assert</span> <span class="n">count_items</span><span class="p">(</span><span class="n">n</span><span class="p">)</span> <span class="o">&gt;=</span> <span class="mi">0</span> </code></pre></div> <p>Key points: - Each parametrize tuple becomes a separate test case in the report - Use <code>ids=</code> for human-readable test names instead of <code>input0, input1, ...</code> - Combine multiple <code>@parametrize</code> decorators for combinatorial testing (n*m cases) - Use <code>pytest.param(..., marks=pytest.mark.xfail)</code> to mark expected failures</p>