pytest parametrize for data-driven tests

<p>I have a function handling many edge cases and want to test all of them without a separate test function per case. I want pytest parametrize with multiple inputs and expected outputs including error cases.</p>

<p>Data-driven testing with parametrize:</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">'status,next_status,allowed'</span><span class="p">,</span> <span class="p">[</span> <span class="p">(</span><span class="s1">'pending'</span><span class="p">,</span> <span class="s1">'validated'</span><span class="p">,</span> <span class="kc">True</span><span class="p">),</span> <span class="p">(</span><span class="s1">'validated'</span><span class="p">,</span> <span class="s1">'pending'</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_status_transition</span><span class="p">(</span><span class="n">status</span><span class="p">,</span> <span class="n">next_status</span><span class="p">,</span> <span class="n">allowed</span><span class="p">):</span> <span class="n">result</span> <span class="o">=</span> <span class="n">is_valid_transition</span><span class="p">(</span><span class="n">status</span><span class="p">,</span> <span class="n">next_status</span><span class="p">)</span> <span class="k">assert</span> <span class="n">result</span> <span class="o">==</span> <span class="n">allowed</span> <span class="c1"># Readable IDs:</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,expected'</span><span class="p">,</span> <span class="p">[</span> <span class="n">pytest</span><span class="o">.</span><span class="n">param</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mf">0.0</span><span class="p">,</span> <span class="nb">id</span><span class="o">=</span><span class="s1">'zero-votes'</span><span class="p">),</span> <span class="n">pytest</span><span class="o">.</span><span class="n">param</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mf">0.206</span><span class="p">,</span> <span class="nb">id</span><span class="o">=</span><span class="s1">'one-vote-low-confidence'</span><span class="p">),</span> <span class="n">pytest</span><span class="o">.</span><span class="n">param</span><span class="p">(</span><span class="mi">100</span><span class="p">,</span> <span class="mf">0.963</span><span class="p">,</span> <span class="nb">id</span><span class="o">=</span><span class="s1">'many-votes-high-confidence'</span><span class="p">),</span> <span class="p">])</span> <span class="k">def</span><span class="w"> </span><span class="nf">test_wilson_score</span><span class="p">(</span><span class="n">n</span><span class="p">,</span> <span class="n">expected</span><span class="p">):</span> <span class="k">assert</span> <span class="nb">abs</span><span class="p">(</span><span class="n">wilson_score</span><span class="p">(</span><span class="n">n</span><span class="p">,</span> <span class="n">n</span><span class="p">)</span> <span class="o">-</span> <span class="n">expected</span><span class="p">)</span> <span class="o">&lt;</span> <span class="mf">0.01</span> </code></pre></div> <p>Key points: - Each parametrize tuple becomes a separate test case in the report - Use ids= or pytest.param(..., id=...) for human-readable test names - Combine multiple @parametrize decorators for combinatorial testing - pytest.param(..., marks=pytest.mark.xfail) marks expected failures</p>