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 735 <body class="article">
 736 <div id="header">
 737 <h1>Unit Testing</h1>
 738 <span id="revdate">2024-07-17</span>
 739 </div>
 740 <div id="content">
 741 <div id="preamble">
 742 <div class="sectionbody">
 743 <div class="paragraph"><p>In our current testing environment, we spend a significant amount of effort
 744 crafting end-to-end tests for error conditions that could easily be captured by
 745 unit tests (or we simply forgo some hard-to-setup and rare error conditions).
 746 Unit tests additionally provide stability to the codebase and can simplify
 747 debugging through isolation. Writing unit tests in pure C, rather than with our
 748 current shell/test-tool helper setup, simplifies test setup, simplifies passing
 749 data around (no shell-isms required), and reduces testing runtime by not
 750 spawning a separate process for every test invocation.</p></div>
 751 <div class="paragraph"><p>We believe that a large body of unit tests, living alongside the existing test
 752 suite, will improve code quality for the Git project.</p></div>
 753 </div>
 754 </div>
 755 <div class="sect1">
 756 <h2 id="_definitions">Definitions</h2>
 757 <div class="sectionbody">
 758 <div class="paragraph"><p>For the purposes of this document, we&#8217;ll use <strong>test framework</strong> to refer to
 759 projects that support writing test cases and running tests within the context
 760 of a single executable. <strong>Test harness</strong> will refer to projects that manage
 761 running multiple executables (each of which may contain multiple test cases) and
 762 aggregating their results.</p></div>
 763 <div class="paragraph"><p>In reality, these terms are not strictly defined, and many of the projects
 764 discussed below contain features from both categories.</p></div>
 765 <div class="paragraph"><p>For now, we will evaluate projects solely on their framework features. Since we
 766 are relying on having TAP output (see below), we can assume that any framework
 767 can be made to work with a harness that we can choose later.</p></div>
 768 </div>
 769 </div>
 770 <div class="sect1">
 771 <h2 id="_summary">Summary</h2>
 772 <div class="sectionbody">
 773 <div class="paragraph"><p>We believe the best way forward is to implement a custom TAP framework for the
 774 Git project. We use a version of the framework originally proposed in
 775 <a href="https://lore.kernel.org/git/c902a166-98ce-afba-93f2-ea6027557176@gmail.com/">1</a>.</p></div>
 776 <div class="paragraph"><p>See the <a href="#framework-selection">Framework Selection</a> section below for the
 777 rationale behind this decision.</p></div>
 778 </div>
 779 </div>
 780 <div class="sect1">
 781 <h2 id="_choosing_a_test_harness">Choosing a test harness</h2>
 782 <div class="sectionbody">
 783 <div class="paragraph"><p>During upstream discussion, it was occasionally noted that <code>prove</code> provides many
 784 convenient features, such as scheduling slower tests first, or re-running
 785 previously failed tests.</p></div>
 786 <div class="paragraph"><p>While we already support the use of <code>prove</code> as a test harness for the shell
 787 tests, it is not strictly required. The t/Makefile allows running shell tests
 788 directly (though with interleaved output if parallelism is enabled). Git
 789 developers who wish to use <code>prove</code> as a more advanced harness can do so by
 790 setting DEFAULT_TEST_TARGET=prove in their config.mak.</p></div>
 791 <div class="paragraph"><p>We will follow a similar approach for unit tests: by default the test
 792 executables will be run directly from the t/Makefile, but <code>prove</code> can be
 793 configured with DEFAULT_UNIT_TEST_TARGET=prove.</p></div>
 794 </div>
 795 </div>
 796 <div class="sect1">
 797 <h2 id="framework-selection">Framework selection</h2>
 798 <div class="sectionbody">
 799 <div class="paragraph"><p>There are a variety of features we can use to rank the candidate frameworks, and
 800 those features have different priorities:</p></div>
 801 <div class="ulist"><ul>
 802 <li>
 803 <p>
 804 Critical features: we probably won&#8217;t consider a framework without these
 805 </p>
 806 <div class="ulist"><ul>
 807 <li>
 808 <p>
 809 Can we legally / easily use the project?
 810 </p>
 811 <div class="ulist"><ul>
 812 <li>
 813 <p>
 814 <a href="#license">License</a>
 815 </p>
 816 </li>
 817 <li>
 818 <p>
 819 <a href="#vendorable-or-ubiquitous">Vendorable or ubiquitous</a>
 820 </p>
 821 </li>
 822 <li>
 823 <p>
 824 <a href="#maintainable-extensible">Maintainable / extensible</a>
 825 </p>
 826 </li>
 827 <li>
 828 <p>
 829 <a href="#major-platform-support">Major platform support</a>
 830 </p>
 831 </li>
 832 </ul></div>
 833 </li>
 834 <li>
 835 <p>
 836 Does the project support our bare-minimum needs?
 837 </p>
 838 <div class="ulist"><ul>
 839 <li>
 840 <p>
 841 <a href="#tap-support">TAP support</a>
 842 </p>
 843 </li>
 844 <li>
 845 <p>
 846 <a href="#diagnostic-output">Diagnostic output</a>
 847 </p>
 848 </li>
 849 <li>
 850 <p>
 851 <a href="#runtime-skippable-tests">Runtime-skippable tests</a>
 852 </p>
 853 </li>
 854 </ul></div>
 855 </li>
 856 </ul></div>
 857 </li>
 858 <li>
 859 <p>
 860 Nice-to-have features:
 861 </p>
 862 <div class="ulist"><ul>
 863 <li>
 864 <p>
 865 <a href="#parallel-execution">Parallel execution</a>
 866 </p>
 867 </li>
 868 <li>
 869 <p>
 870 <a href="#mock-support">Mock support</a>
 871 </p>
 872 </li>
 873 <li>
 874 <p>
 875 <a href="#signal-error-handling">Signal &amp; error-handling</a>
 876 </p>
 877 </li>
 878 </ul></div>
 879 </li>
 880 <li>
 881 <p>
 882 Tie-breaker stats
 883 </p>
 884 <div class="ulist"><ul>
 885 <li>
 886 <p>
 887 <a href="#project-kloc">Project KLOC</a>
 888 </p>
 889 </li>
 890 <li>
 891 <p>
 892 <a href="#adoption">Adoption</a>
 893 </p>
 894 </li>
 895 </ul></div>
 896 </li>
 897 </ul></div>
 898 <div class="sect2">
 899 <h3 id="license">License</h3>
 900 <div class="paragraph"><p>We must be able to legally use the framework in connection with Git. As Git is
 901 licensed only under GPLv2, we must eliminate any LGPLv3, GPLv3, or Apache 2.0
 902 projects.</p></div>
 903 </div>
 904 <div class="sect2">
 905 <h3 id="vendorable-or-ubiquitous">Vendorable or ubiquitous</h3>
 906 <div class="paragraph"><p>We want to avoid forcing Git developers to install new tools just to run unit
 907 tests. Any prospective frameworks and harnesses must either be vendorable
 908 (meaning, we can copy their source directly into Git&#8217;s repository), or so
 909 ubiquitous that it is reasonable to expect that most developers will have the
 910 tools installed already.</p></div>
 911 </div>
 912 <div class="sect2">
 913 <h3 id="maintainable-extensible">Maintainable / extensible</h3>
 914 <div class="paragraph"><p>It is unlikely that any pre-existing project perfectly fits our needs, so any
 915 project we select will need to be actively maintained and open to accepting
 916 changes. Alternatively, assuming we are vendoring the source into our repo, it
 917 must be simple enough that Git developers can feel comfortable making changes as
 918 needed to our version.</p></div>
 919 <div class="paragraph"><p>In the comparison table below, "True" means that the framework seems to have
 920 active developers, that it is simple enough that Git developers can make changes
 921 to it, and that the project seems open to accepting external contributions (or
 922 that it is vendorable). "Partial" means that at least one of the above
 923 conditions holds.</p></div>
 924 </div>
 925 <div class="sect2">
 926 <h3 id="major-platform-support">Major platform support</h3>
 927 <div class="paragraph"><p>At a bare minimum, unit-testing must work on Linux, MacOS, and Windows.</p></div>
 928 <div class="paragraph"><p>In the comparison table below, "True" means that it works on all three major
 929 platforms with no issues. "Partial" means that there may be annoyances on one or
 930 more platforms, but it is still usable in principle.</p></div>
 931 </div>
 932 <div class="sect2">
 933 <h3 id="tap-support">TAP support</h3>
 934 <div class="paragraph"><p>The <a href="https://testanything.org/">Test Anything Protocol</a> is a text-based interface
 935 that allows tests to communicate with a test harness. It is already used by
 936 Git&#8217;s integration test suite. Supporting TAP output is a mandatory feature for
 937 any prospective test framework.</p></div>
 938 <div class="paragraph"><p>In the comparison table below, "True" means this is natively supported.
 939 "Partial" means TAP output must be generated by post-processing the native
 940 output.</p></div>
 941 <div class="paragraph"><p>Frameworks that do not have at least Partial support will not be evaluated
 942 further.</p></div>
 943 </div>
 944 <div class="sect2">
 945 <h3 id="diagnostic-output">Diagnostic output</h3>
 946 <div class="paragraph"><p>When a test case fails, the framework must generate enough diagnostic output to
 947 help developers find the appropriate test case in source code in order to debug
 948 the failure.</p></div>
 949 </div>
 950 <div class="sect2">
 951 <h3 id="runtime-skippable-tests">Runtime-skippable tests</h3>
 952 <div class="paragraph"><p>Test authors may wish to skip certain test cases based on runtime circumstances,
 953 so the framework should support this.</p></div>
 954 </div>
 955 <div class="sect2">
 956 <h3 id="parallel-execution">Parallel execution</h3>
 957 <div class="paragraph"><p>Ideally, we will build up a significant collection of unit test cases, most
 958 likely split across multiple executables. It will be necessary to run these
 959 tests in parallel to enable fast develop-test-debug cycles.</p></div>
 960 <div class="paragraph"><p>In the comparison table below, "True" means that individual test cases within a
 961 single test executable can be run in parallel. We assume that executable-level
 962 parallelism can be handled by the test harness.</p></div>
 963 </div>
 964 <div class="sect2">
 965 <h3 id="mock-support">Mock support</h3>
 966 <div class="paragraph"><p>Unit test authors may wish to test code that interacts with objects that may be
 967 inconvenient to handle in a test (e.g. interacting with a network service).
 968 Mocking allows test authors to provide a fake implementation of these objects
 969 for more convenient tests.</p></div>
 970 </div>
 971 <div class="sect2">
 972 <h3 id="signal-error-handling">Signal &amp; error handling</h3>
 973 <div class="paragraph"><p>The test framework should fail gracefully when test cases are themselves buggy
 974 or when they are interrupted by signals during runtime.</p></div>
 975 </div>
 976 <div class="sect2">
 977 <h3 id="project-kloc">Project KLOC</h3>
 978 <div class="paragraph"><p>The size of the project, in thousands of lines of code as measured by
 979 <a href="https://dwheeler.com/sloccount/">sloccount</a> (rounded up to the next multiple of
 980 1,000). As a tie-breaker, we probably prefer a project with fewer LOC.</p></div>
 981 </div>
 982 <div class="sect2">
 983 <h3 id="adoption">Adoption</h3>
 984 <div class="paragraph"><p>As a tie-breaker, we prefer a more widely-used project. We use the number of
 985 GitHub / GitLab stars to estimate this.</p></div>
 986 </div>
 987 <div class="sect2">
 988 <h3 id="_comparison">Comparison</h3>
 989 <div class="tableblock">
 990 <table rules="all"
 991 width="33%"
 992 frame="border"
 993 cellspacing="0" cellpadding="4">
 994 <col width="4%" />
 995 <col width="4%" />
 996 <col width="4%" />
 997 <col width="4%" />
 998 <col width="4%" />
 999 <col width="4%" />
1000 <col width="4%" />
1001 <col width="4%" />
1002 <col width="4%" />
1003 <col width="4%" />
1004 <col width="4%" />
1005 <col width="4%" />
1006 <col width="4%" />
1007 <col width="4%" />
1008 <col width="4%" />
1009 <col width="4%" />
1010 <col width="4%" />
1011 <col width="4%" />
1012 <col width="4%" />
1013 <col width="4%" />
1014 <col width="4%" />
1015 <col width="4%" />
1016 <col width="4%" />
1017 <col width="4%" />
1018 <col width="4%" />
1019 <thead>
1020 <tr>
1021 <th align="left" valign="top">Framework</th>
1022 <th align="left" valign="top"><a href="#license">License</a></th>
1023 <th align="left" valign="top"><a href="#vendorable-or-ubiquitous">Vendorable or ubiquitous</a></th>
1024 <th align="left" valign="top"><a href="#maintainable-extensible">Maintainable / extensible</a></th>
1025 <th align="left" valign="top"><a href="#major-platform-support">Major platform support</a></th>
1026 <th align="left" valign="top"><a href="#tap-support">TAP support</a></th>
1027 <th align="left" valign="top"><a href="#diagnostic-output">Diagnostic output</a></th>
1028 <th align="left" valign="top"><a href="#runtime--skippable-tests">Runtime- skippable tests</a></th>
1029 <th align="left" valign="top"><a href="#parallel-execution">Parallel execution</a></th>
1030 <th align="left" valign="top"><a href="#mock-support">Mock support</a></th>
1031 <th align="left" valign="top"><a href="#signal-error-handling">Signal &amp; error handling</a></th>
1032 <th align="left" valign="top"><a href="#project-kloc">Project KLOC</a></th>
1033 <th align="left" valign="top"><a href="#adoption">Adoption</a></th>
1034 </tr>
1035 </thead>
1036 <tbody>
1037 <tr>
1038 <td align="left" valign="top"><p class="table"><a href="https://lore.kernel.org/git/c902a166-98ce-afba-93f2-ea6027557176@gmail.com/">Custom Git impl.</a></p></td>
1039 <td align="left" valign="top"><p class="table"><span class="lime-background">GPL v2</span></p></td>
1040 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1041 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1042 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1043 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1044 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1045 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1046 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1047 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1048 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1049 <td align="left" valign="top"><p class="table">1</p></td>
1050 <td align="left" valign="top"><p class="table">0</p></td>
1051 </tr>
1052 <tr>
1053 <td align="left" valign="top"><p class="table"><a href="https://github.com/silentbicycle/greatest">Greatest</a></p></td>
1054 <td align="left" valign="top"><p class="table"><span class="lime-background">ISC</span></p></td>
1055 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1056 <td align="left" valign="top"><p class="table"><span class="yellow-background">Partial</span></p></td>
1057 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1058 <td align="left" valign="top"><p class="table"><span class="yellow-background">Partial</span></p></td>
1059 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1060 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1061 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1062 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1063 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1064 <td align="left" valign="top"><p class="table">3</p></td>
1065 <td align="left" valign="top"><p class="table">1400</p></td>
1066 </tr>
1067 <tr>
1068 <td align="left" valign="top"><p class="table"><a href="https://github.com/Snaipe/Criterion">Criterion</a></p></td>
1069 <td align="left" valign="top"><p class="table"><span class="lime-background">MIT</span></p></td>
1070 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1071 <td align="left" valign="top"><p class="table"><span class="yellow-background">Partial</span></p></td>
1072 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1073 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1074 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1075 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1076 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1077 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1078 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1079 <td align="left" valign="top"><p class="table">19</p></td>
1080 <td align="left" valign="top"><p class="table">1800</p></td>
1081 </tr>
1082 <tr>
1083 <td align="left" valign="top"><p class="table"><a href="https://github.com/rra/c-tap-harness/">C TAP</a></p></td>
1084 <td align="left" valign="top"><p class="table"><span class="lime-background">Expat</span></p></td>
1085 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1086 <td align="left" valign="top"><p class="table"><span class="yellow-background">Partial</span></p></td>
1087 <td align="left" valign="top"><p class="table"><span class="yellow-background">Partial</span></p></td>
1088 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1089 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1090 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1091 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1092 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1093 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1094 <td align="left" valign="top"><p class="table">4</p></td>
1095 <td align="left" valign="top"><p class="table">33</p></td>
1096 </tr>
1097 <tr>
1098 <td align="left" valign="top"><p class="table"><a href="https://libcheck.github.io/check/">Check</a></p></td>
1099 <td align="left" valign="top"><p class="table"><span class="lime-background">LGPL v2.1</span></p></td>
1100 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1101 <td align="left" valign="top"><p class="table"><span class="yellow-background">Partial</span></p></td>
1102 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1103 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1104 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1105 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1106 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1107 <td align="left" valign="top"><p class="table"><span class="red-background">False</span></p></td>
1108 <td align="left" valign="top"><p class="table"><span class="lime-background">True</span></p></td>
1109 <td align="left" valign="top"><p class="table">17</p></td>
1110 <td align="left" valign="top"><p class="table">973</p></td>
1111 </tr>
1112 </tbody>
1113 </table>
1114 </div>
1115 </div>
1116 <div class="sect2">
1117 <h3 id="_additional_framework_candidates">Additional framework candidates</h3>
1118 <div class="paragraph"><p>Several suggested frameworks have been eliminated from consideration:</p></div>
1119 <div class="ulist"><ul>
1120 <li>
1121 <p>
1122 Incompatible licenses:
1123 </p>
1124 <div class="ulist"><ul>
1125 <li>
1126 <p>
1127 <a href="https://github.com/zorgnax/libtap">libtap</a> (LGPL v3)
1128 </p>
1129 </li>
1130 <li>
1131 <p>
1132 <a href="https://cmocka.org/">cmocka</a> (Apache 2.0)
1133 </p>
1134 </li>
1135 </ul></div>
1136 </li>
1137 <li>
1138 <p>
1139 Missing source: <a href="https://www.kindahl.net/mytap/doc/index.html">MyTap</a>
1140 </p>
1141 </li>
1142 <li>
1143 <p>
1144 No TAP support:
1145 </p>
1146 <div class="ulist"><ul>
1147 <li>
1148 <p>
1149 <a href="https://nemequ.github.io/munit/">µnit</a>
1150 </p>
1151 </li>
1152 <li>
1153 <p>
1154 <a href="https://github.com/google/cmockery">cmockery</a>
1155 </p>
1156 </li>
1157 <li>
1158 <p>
1159 <a href="https://github.com/lpabon/cmockery2">cmockery2</a>
1160 </p>
1161 </li>
1162 <li>
1163 <p>
1164 <a href="https://github.com/ThrowTheSwitch/Unity">Unity</a>
1165 </p>
1166 </li>
1167 <li>
1168 <p>
1169 <a href="https://github.com/siu/minunit">minunit</a>
1170 </p>
1171 </li>
1172 <li>
1173 <p>
1174 <a href="https://cunit.sourceforge.net/">CUnit</a>
1175 </p>
1176 </li>
1177 </ul></div>
1178 </li>
1179 </ul></div>
1180 </div>
1181 </div>
1182 </div>
1183 <div class="sect1">
1184 <h2 id="_milestones">Milestones</h2>
1185 <div class="sectionbody">
1186 <div class="ulist"><ul>
1187 <li>
1188 <p>
1189 Add useful tests of library-like code
1190 </p>
1191 </li>
1192 <li>
1193 <p>
1194 Integrate with
1195   <a href="https://lore.kernel.org/git/20230502211454.1673000-1-calvinwan@google.com/">stdlib
1196   work</a>
1197 </p>
1198 </li>
1199 <li>
1200 <p>
1201 Run alongside regular <code>make test</code> target
1202 </p>
1203 </li>
1204 </ul></div>
1205 </div>
1206 </div>
1207 </div>
1208 <div id="footnotes"><hr /></div>
1209 <div id="footer">
1210 <div id="footer-text">
1211 Last updated
1212  2023-12-09 17:40:53 PST
1213 </div>
1214 </div>
1215 </body>
1216 </html>