Allow test sharding for e.g. Bazel test sharding feature

This greatly simplifies running Catch2 tests in single binary
in parallel from external test runners. Instead of having to
shard the tests by tags/test names, an external test runner
can now just ask for test shard 2 (out of X), and execute that
in single process, without having to know what tests are actually
in the shard.

Note that sharding also applies to test listing, and happens after
tests were ordered according to the `--order` feature.

docs/command-line.md

@@ -29,6 +29,7 @@
 [Specify the section to run](#specify-the-section-to-run)<br>
 [Filenames as tags](#filenames-as-tags)<br>
 [Override output colouring](#override-output-colouring)<br>
+[Test Sharding](#test-sharding)<br>
 
 Catch works quite nicely without any command line options at all - but for those times when you want greater control the following options are available.
 Click one of the following links to take you straight to that option - or scroll on to browse the available options.
@@ -67,6 +68,8 @@ Click one of the following links to take you straight to that option - or scroll
 <a href="#benchmark-no-analysis">                       `    --benchmark-no-analysis`</a><br />
 <a href="#benchmark-warmup-time">                       `    --benchmark-warmup-time`</a><br />
 <a href="#use-colour">                                  `    --use-colour`</a><br />
+<a href="#test-sharding">                               `    --shard-count`</a><br />
+<a href="#test-sharding">                               `    --shard-index`</a><br />
 
 </br>
 
@@ -425,6 +428,20 @@ processing of output.
 `--use-colour yes` forces coloured output, `--use-colour no` disables coloured
 output. The default behaviour is `--use-colour auto`.
 
+<a id="test-sharding"></a>
+## Test Sharding
+<pre>--shard-count <#number of shards>, --shard-index <#shard index to run></pre>
+
+> [Introduced](https://github.com/catchorg/Catch2/pull/2257) in Catch2 X.Y.Z.
+
+When `--shard-count <#number of shards>` is used, the tests to execute will be split evenly in to the given number of sets,
+identified by indicies starting at 0. The tests in the set given by `--shard-index <#shard index to run>` will be executed.
+The default shard count is `1`, and the default index to run is `0`. It is an error to specify a shard index greater than
+the number of shards.
+
+This is useful when you want to split test execution across multiple processes, as is done with [Bazel test sharding](https://docs.bazel.build/versions/main/test-encyclopedia.html#test-sharding). 
+
+
 ---
 
 [Home](Readme.md#top)

src/catch2/catch_all.hpp

@@ -85,6 +85,7 @@
 #include <catch2/internal/catch_result_type.hpp>
 #include <catch2/internal/catch_run_context.hpp>
 #include <catch2/internal/catch_section.hpp>
+#include <catch2/internal/catch_sharding.hpp>
 #include <catch2/internal/catch_singletons.hpp>
 #include <catch2/internal/catch_source_line_info.hpp>
 #include <catch2/internal/catch_startup_exception_registry.hpp>

src/catch2/catch_config.cpp

@@ -73,6 +73,8 @@ namespace Catch {
     double Config::minDuration() const                 { return m_data.minDuration; }
     TestRunOrder Config::runOrder() const              { return m_data.runOrder; }
     uint32_t Config::rngSeed() const                   { return m_data.rngSeed; }
+    unsigned int Config::shardCount() const            { return m_data.shardCount; }
+    unsigned int Config::shardIndex() const            { return m_data.shardIndex; }
     UseColour Config::useColour() const                { return m_data.useColour; }
     bool Config::shouldDebugBreak() const              { return m_data.shouldDebugBreak; }
     int Config::abortAfter() const                     { return m_data.abortAfter; }

src/catch2/catch_config.hpp

@@ -37,6 +37,9 @@ namespace Catch {
         int abortAfter = -1;
         uint32_t rngSeed = generateRandomSeed(GenerateFrom::Default);
 
+        unsigned int shardCount = 1;
+        unsigned int shardIndex = 0;
+
         bool benchmarkNoAnalysis = false;
         unsigned int benchmarkSamples = 100;
         double benchmarkConfidenceInterval = 0.95;
@@ -99,6 +102,8 @@ namespace Catch {
         double minDuration() const override;
         TestRunOrder runOrder() const override;
         uint32_t rngSeed() const override;
+        unsigned int shardCount() const override;
+        unsigned int shardIndex() const override;
         UseColour useColour() const override;
         bool shouldDebugBreak() const override;
         int abortAfter() const override;

src/catch2/catch_session.cpp

@@ -16,6 +16,7 @@
 #include <catch2/catch_version.hpp>
 #include <catch2/interfaces/catch_interfaces_reporter.hpp>
 #include <catch2/internal/catch_startup_exception_registry.hpp>
+#include <catch2/internal/catch_sharding.hpp>
 #include <catch2/internal/catch_textflow.hpp>
 #include <catch2/internal/catch_windows_h_proxy.hpp>
 #include <catch2/reporters/catch_reporter_listening.hpp>
@@ -72,6 +73,8 @@ namespace Catch {
                     for (auto const& match : m_matches)
                         m_tests.insert(match.tests.begin(), match.tests.end());
                 }
+
+                m_tests = createShard(m_tests, m_config->shardCount(), m_config->shardIndex());
             }
 
             Totals execute() {
@@ -171,6 +174,7 @@ namespace Catch {
             return 1;
 
         auto result = m_cli.parse( Clara::Args( argc, argv ) );
+
         if( !result ) {
             config();
             getCurrentMutableContext().setConfig(m_config.get());
@@ -253,6 +257,12 @@ namespace Catch {
         if( m_startupExceptions )
             return 1;
 
+
+        if( m_configData.shardIndex >= m_configData.shardCount ) {
+            Catch::cerr() << "The shard count (" << m_configData.shardCount << ") must be greater than the shard index ("  << m_configData.shardIndex << ")\n" << std::flush;
+            return 1;
+        }
+
         if (m_configData.showHelp || m_configData.libIdentify) {
             return 0;
         }

src/catch2/interfaces/catch_interfaces_config.hpp

@@ -74,6 +74,8 @@ namespace Catch {
         virtual std::vector<std::string> const& getTestsOrTags() const = 0;
         virtual TestRunOrder runOrder() const = 0;
         virtual uint32_t rngSeed() const = 0;
+        virtual unsigned int shardCount() const = 0;
+        virtual unsigned int shardIndex() const = 0;
         virtual UseColour useColour() const = 0;
         virtual std::vector<std::string> const& getSectionsToRun() const = 0;
         virtual Verbosity verbosity() const = 0;

src/catch2/internal/catch_commandline.cpp

@@ -149,6 +149,15 @@ namespace Catch {
                 return ParserResult::runtimeError( "Unrecognized reporter, '" + reporter + "'. Check available with --list-reporters" );
             return ParserResult::ok( ParseResultType::Matched );
         };
+        auto const setShardCount = [&]( std::string const& shardCount ) {
+            auto result = Clara::Detail::convertInto( shardCount, config.shardCount );
+
+            if (config.shardCount == 0) {
+                return ParserResult::runtimeError( "The shard count must be greater than 0" );
+            } else {
+                return result;
+            }
+        };
 
         auto cli
             = ExeName( config.processName )
@@ -240,6 +249,12 @@ namespace Catch {
             | Opt( config.benchmarkWarmupTime, "benchmarkWarmupTime" )
                 ["--benchmark-warmup-time"]
                 ( "amount of time in milliseconds spent on warming up each test (default: 100)" )
+            | Opt( setShardCount, "shard count" )
+                ["--shard-count"]
+                ( "split the tests to execute into this many groups" )
+            | Opt( config.shardIndex, "shard index" )
+                ["--shard-index"]
+                ( "index of the group of tests to execute (see --shard-count)" )
             | Arg( config.testsOrTags, "test name|pattern|tags" )
                 ( "which test or tests to use" );
 

src/catch2/internal/catch_sharding.hpp

@@ -0,0 +1,41 @@
+
+//              Copyright Catch2 Authors
+// Distributed under the Boost Software License, Version 1.0.
+//   (See accompanying file LICENSE_1_0.txt or copy at
+//        https://www.boost.org/LICENSE_1_0.txt)
+
+// SPDX-License-Identifier: BSL-1.0
+#ifndef CATCH_SHARDING_HPP_INCLUDED
+#define CATCH_SHARDING_HPP_INCLUDED
+
+#include <catch2/catch_session.hpp>
+
+#include <cmath>
+
+namespace Catch {
+
+    template<typename Container>
+    Container createShard(Container const& container, std::size_t const shardCount, std::size_t const shardIndex) {
+        assert(shardCount > shardIndex);
+
+        if (shardCount == 1) {
+            return container;
+        }
+
+        const std::size_t totalTestCount = container.size();
+
+        const std::size_t shardSize = totalTestCount / shardCount;
+        const std::size_t leftoverTests = totalTestCount % shardCount;
+
+        const std::size_t startIndex = shardIndex * shardSize + (std::min)(shardIndex, leftoverTests);
+        const std::size_t endIndex = (shardIndex + 1) * shardSize + (std::min)(shardIndex + 1, leftoverTests);
+
+        auto startIterator = std::next(container.begin(), startIndex);
+        auto endIterator = std::next(container.begin(), endIndex);
+
+        return Container(startIterator, endIterator);
+    }
+
+}
+
+#endif // CATCH_SHARDING_HPP_INCLUDED

src/catch2/internal/catch_test_case_registry_impl.cpp

@@ -12,6 +12,7 @@
 #include <catch2/interfaces/catch_interfaces_registry_hub.hpp>
 #include <catch2/internal/catch_random_number_generator.hpp>
 #include <catch2/internal/catch_run_context.hpp>
+#include <catch2/internal/catch_sharding.hpp>
 #include <catch2/catch_test_case_info.hpp>
 #include <catch2/catch_test_spec.hpp>
 #include <catch2/internal/catch_move_and_forward.hpp>
@@ -135,7 +136,7 @@ namespace {
                 filtered.push_back(testCase);
             }
         }
-        return filtered;
+        return createShard(filtered, config.shardCount(), config.shardIndex());
     }
     std::vector<TestCaseHandle> const& getAllTestCasesSorted( IConfig const& config ) {
         return getRegistryHub().getTestCaseRegistry().getAllTestsSorted( config );

tests/CMakeLists.txt

@@ -87,6 +87,7 @@ set(TEST_SOURCES
         ${SELF_TEST_DIR}/IntrospectiveTests/RandomNumberGeneration.tests.cpp
         ${SELF_TEST_DIR}/IntrospectiveTests/Reporters.tests.cpp
         ${SELF_TEST_DIR}/IntrospectiveTests/Tag.tests.cpp
+        ${SELF_TEST_DIR}/IntrospectiveTests/Sharding.tests.cpp
         ${SELF_TEST_DIR}/IntrospectiveTests/String.tests.cpp
         ${SELF_TEST_DIR}/IntrospectiveTests/StringManip.tests.cpp
         ${SELF_TEST_DIR}/IntrospectiveTests/Xml.tests.cpp
@@ -310,6 +311,7 @@ set_tests_properties(TagAlias PROPERTIES
 add_test(NAME RandomTestOrdering COMMAND ${PYTHON_EXECUTABLE}
   ${CATCH_DIR}/tests/TestScripts/testRandomOrder.py $<TARGET_FILE:SelfTest>)
 
+
 add_test(NAME CheckConvenienceHeaders
   COMMAND
     ${PYTHON_EXECUTABLE} ${CATCH_DIR}/tools/scripts/checkConvenienceHeaders.py

tests/ExtraTests/CMakeLists.txt

@@ -8,6 +8,22 @@ project( Catch2ExtraTests LANGUAGES CXX )
 
 message( STATUS "Extra tests included" )
 
+
+add_test(
+  NAME TestShardingIntegration
+  COMMAND ${PYTHON_EXECUTABLE} ${CATCH_DIR}/tests/TestScripts/testSharding.py $<TARGET_FILE:SelfTest>
+)
+
+add_test(
+  NAME TestSharding::OverlyLargeShardIndex
+  COMMAND $<TARGET_FILE:SelfTest>  --shard-index 5 --shard-count 5
+)
+set_tests_properties(
+    TestSharding::OverlyLargeShardIndex
+  PROPERTIES
+    PASS_REGULAR_EXPRESSION "The shard count \\(5\\) must be greater than the shard index \\(5\\)"
+)
+
 # The MinDuration reporting tests do not need separate compilation, but
 # they have non-trivial execution time, so they are categorized as
 # extra tests, so that they are run less.

tests/SelfTest/Baselines/compact.sw.approved.txt

@@ -1273,6 +1273,12 @@ CmdLine.tests.cpp:<line number>: passed: cli.parse({ "test", "--benchmark-no-ana
 CmdLine.tests.cpp:<line number>: passed: config.benchmarkNoAnalysis for: true
 CmdLine.tests.cpp:<line number>: passed: cli.parse({ "test", "--benchmark-warmup-time=10" }) for: {?}
 CmdLine.tests.cpp:<line number>: passed: config.benchmarkWarmupTime == 10 for: 10 == 10
+CmdLine.tests.cpp:<line number>: passed: cli.parse({ "test", "--shard-count=8"}) for: {?}
+CmdLine.tests.cpp:<line number>: passed: config.shardCount == 8 for: 8 == 8
+CmdLine.tests.cpp:<line number>: passed: cli.parse({ "test", "--shard-index=2"}) for: {?}
+CmdLine.tests.cpp:<line number>: passed: config.shardIndex == 2 for: 2 == 2
+CmdLine.tests.cpp:<line number>: passed: !result for: true
+CmdLine.tests.cpp:<line number>: passed: result.errorMessage(), ContainsSubstring( "The shard count must be greater than 0" ) for: "The shard count must be greater than 0" contains: "The shard count must be greater than 0"
 Misc.tests.cpp:<line number>: passed: std::tuple_size<TestType>::value >= 1 for: 3 >= 1
 Misc.tests.cpp:<line number>: passed: std::tuple_size<TestType>::value >= 1 for: 2 >= 1
 Misc.tests.cpp:<line number>: passed: std::tuple_size<TestType>::value >= 1 for: 1 >= 1

tests/SelfTest/Baselines/console.std.approved.txt

@@ -1427,5 +1427,5 @@ due to unexpected exception with message:
 
 ===============================================================================
 test cases:  373 |  296 passed |  70 failed |  7 failed as expected
-assertions: 2115 | 1959 passed | 129 failed | 27 failed as expected
+assertions: 2121 | 1965 passed | 129 failed | 27 failed as expected
 

tests/SelfTest/Baselines/console.sw.approved.txt

@@ -9390,6 +9390,61 @@ CmdLine.tests.cpp:<line number>: PASSED:
 with expansion:
   10 == 10
 
+-------------------------------------------------------------------------------
+Process can be configured on command line
+  Sharding options
+  shard-count
+-------------------------------------------------------------------------------
+CmdLine.tests.cpp:<line number>
+...............................................................................
+
+CmdLine.tests.cpp:<line number>: PASSED:
+  CHECK( cli.parse({ "test", "--shard-count=8"}) )
+with expansion:
+  {?}
+
+CmdLine.tests.cpp:<line number>: PASSED:
+  REQUIRE( config.shardCount == 8 )
+with expansion:
+  8 == 8
+
+-------------------------------------------------------------------------------
+Process can be configured on command line
+  Sharding options
+  shard-index
+-------------------------------------------------------------------------------
+CmdLine.tests.cpp:<line number>
+...............................................................................
+
+CmdLine.tests.cpp:<line number>: PASSED:
+  CHECK( cli.parse({ "test", "--shard-index=2"}) )
+with expansion:
+  {?}
+
+CmdLine.tests.cpp:<line number>: PASSED:
+  REQUIRE( config.shardIndex == 2 )
+with expansion:
+  2 == 2
+
+-------------------------------------------------------------------------------
+Process can be configured on command line
+  Sharding options
+  Zero shard-count
+-------------------------------------------------------------------------------
+CmdLine.tests.cpp:<line number>
+...............................................................................
+
+CmdLine.tests.cpp:<line number>: PASSED:
+  CHECK( !result )
+with expansion:
+  true
+
+CmdLine.tests.cpp:<line number>: PASSED:
+  CHECK_THAT( result.errorMessage(), ContainsSubstring( "The shard count must be greater than 0" ) )
+with expansion:
+  "The shard count must be greater than 0" contains: "The shard count must be
+  greater than 0"
+
 -------------------------------------------------------------------------------
 Product with differing arities - std::tuple<int, double, float>
 -------------------------------------------------------------------------------
@@ -17040,5 +17095,5 @@ Misc.tests.cpp:<line number>: PASSED:
 
 ===============================================================================
 test cases:  373 |  280 passed |  86 failed |  7 failed as expected
-assertions: 2132 | 1959 passed | 146 failed | 27 failed as expected
+assertions: 2138 | 1965 passed | 146 failed | 27 failed as expected
 

tests/SelfTest/Baselines/junit.sw.approved.txt

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <testsuitesloose text artifact
 >
-  <testsuite name="<exe-name>" errors="17" failures="129" tests="2132" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
+  <testsuite name="<exe-name>" errors="17" failures="129" tests="2138" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
     <properties>
       <property name="random-seed" value="1"/>
       <property name="filters" value="~[!nonportable]~[!benchmark]~[approvals] *"/>
@@ -1096,6 +1096,9 @@ Message.tests.cpp:<line number>
     <testcase classname="<exe-name>.global" name="Process can be configured on command line/Benchmark options/confidence-interval" time="{duration}" status="run"/>
     <testcase classname="<exe-name>.global" name="Process can be configured on command line/Benchmark options/no-analysis" time="{duration}" status="run"/>
     <testcase classname="<exe-name>.global" name="Process can be configured on command line/Benchmark options/warmup-time" time="{duration}" status="run"/>
+    <testcase classname="<exe-name>.global" name="Process can be configured on command line/Sharding options/shard-count" time="{duration}" status="run"/>
+    <testcase classname="<exe-name>.global" name="Process can be configured on command line/Sharding options/shard-index" time="{duration}" status="run"/>
+    <testcase classname="<exe-name>.global" name="Process can be configured on command line/Sharding options/Zero shard-count" time="{duration}" status="run"/>
     <testcase classname="<exe-name>.global" name="Product with differing arities - std::tuple&lt;int, double, float>" time="{duration}" status="run"/>
     <testcase classname="<exe-name>.global" name="Product with differing arities - std::tuple&lt;int, double>" time="{duration}" status="run"/>
     <testcase classname="<exe-name>.global" name="Product with differing arities - std::tuple&lt;int>" time="{duration}" status="run"/>

tests/SelfTest/Baselines/sonarqube.sw.approved.txt

@@ -75,6 +75,9 @@
     <testCase name="Process can be configured on command line/Benchmark options/confidence-interval" duration="{duration}"/>
     <testCase name="Process can be configured on command line/Benchmark options/no-analysis" duration="{duration}"/>
     <testCase name="Process can be configured on command line/Benchmark options/warmup-time" duration="{duration}"/>
+    <testCase name="Process can be configured on command line/Sharding options/shard-count" duration="{duration}"/>
+    <testCase name="Process can be configured on command line/Sharding options/shard-index" duration="{duration}"/>
+    <testCase name="Process can be configured on command line/Sharding options/Zero shard-count" duration="{duration}"/>
     <testCase name="Test with special, characters &quot;in name" duration="{duration}"/>
   </file>
   <file path="tests/<exe-name>/IntrospectiveTests/FloatingPoint.tests.cpp">

tests/SelfTest/Baselines/tap.sw.approved.txt

@@ -2468,6 +2468,18 @@ ok {test-number} - config.benchmarkNoAnalysis for: true
 ok {test-number} - cli.parse({ "test", "--benchmark-warmup-time=10" }) for: {?}
 # Process can be configured on command line
 ok {test-number} - config.benchmarkWarmupTime == 10 for: 10 == 10
+# Process can be configured on command line
+ok {test-number} - cli.parse({ "test", "--shard-count=8"}) for: {?}
+# Process can be configured on command line
+ok {test-number} - config.shardCount == 8 for: 8 == 8
+# Process can be configured on command line
+ok {test-number} - cli.parse({ "test", "--shard-index=2"}) for: {?}
+# Process can be configured on command line
+ok {test-number} - config.shardIndex == 2 for: 2 == 2
+# Process can be configured on command line
+ok {test-number} - !result for: true
+# Process can be configured on command line
+ok {test-number} - result.errorMessage(), ContainsSubstring( "The shard count must be greater than 0" ) for: "The shard count must be greater than 0" contains: "The shard count must be greater than 0"
 # Product with differing arities - std::tuple<int, double, float>
 ok {test-number} - std::tuple_size<TestType>::value >= 1 for: 3 >= 1
 # Product with differing arities - std::tuple<int, double>
@@ -4266,5 +4278,5 @@ ok {test-number} - q3 == 23. for: 23.0 == 23.0
 ok {test-number} -
 # xmlentitycheck
 ok {test-number} -
-1..2132
+1..2138
 

tests/SelfTest/Baselines/xml.sw.approved.txt

@@ -11469,6 +11469,72 @@ Nor would this
       </Section>
       <OverallResults successes="2" failures="0" expectedFailures="0"/>
     </Section>
+    <Section name="Sharding options" filename="tests/<exe-name>/IntrospectiveTests/CmdLine.tests.cpp" >
+      <Section name="shard-count" filename="tests/<exe-name>/IntrospectiveTests/CmdLine.tests.cpp" >
+        <Expression success="true" type="CHECK" filename="tests/<exe-name>/IntrospectiveTests/CmdLine.tests.cpp" >
+          <Original>
+            cli.parse({ "test", "--shard-count=8"})
+          </Original>
+          <Expanded>
+            {?}
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="tests/<exe-name>/IntrospectiveTests/CmdLine.tests.cpp" >
+          <Original>
+            config.shardCount == 8
+          </Original>
+          <Expanded>
+            8 == 8
+          </Expanded>
+        </Expression>
+        <OverallResults successes="2" failures="0" expectedFailures="0"/>
+      </Section>
+      <OverallResults successes="2" failures="0" expectedFailures="0"/>
+    </Section>
+    <Section name="Sharding options" filename="tests/<exe-name>/IntrospectiveTests/CmdLine.tests.cpp" >
+      <Section name="shard-index" filename="tests/<exe-name>/IntrospectiveTests/CmdLine.tests.cpp" >
+        <Expression success="true" type="CHECK" filename="tests/<exe-name>/IntrospectiveTests/CmdLine.tests.cpp" >
+          <Original>
+            cli.parse({ "test", "--shard-index=2"})
+          </Original>
+          <Expanded>
+            {?}
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="tests/<exe-name>/IntrospectiveTests/CmdLine.tests.cpp" >
+          <Original>
+            config.shardIndex == 2
+          </Original>
+          <Expanded>
+            2 == 2
+          </Expanded>
+        </Expression>
+        <OverallResults successes="2" failures="0" expectedFailures="0"/>
+      </Section>
+      <OverallResults successes="2" failures="0" expectedFailures="0"/>
+    </Section>
+    <Section name="Sharding options" filename="tests/<exe-name>/IntrospectiveTests/CmdLine.tests.cpp" >
+      <Section name="Zero shard-count" filename="tests/<exe-name>/IntrospectiveTests/CmdLine.tests.cpp" >
+        <Expression success="true" type="CHECK" filename="tests/<exe-name>/IntrospectiveTests/CmdLine.tests.cpp" >
+          <Original>
+            !result
+          </Original>
+          <Expanded>
+            true
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="CHECK_THAT" filename="tests/<exe-name>/IntrospectiveTests/CmdLine.tests.cpp" >
+          <Original>
+            result.errorMessage(), ContainsSubstring( "The shard count must be greater than 0" )
+          </Original>
+          <Expanded>
+            "The shard count must be greater than 0" contains: "The shard count must be greater than 0"
+          </Expanded>
+        </Expression>
+        <OverallResults successes="2" failures="0" expectedFailures="0"/>
+      </Section>
+      <OverallResults successes="2" failures="0" expectedFailures="0"/>
+    </Section>
     <OverallResult success="true"/>
   </TestCase>
   <TestCase name="Product with differing arities - std::tuple&lt;int, double, float>" tags="[product][template]" filename="tests/<exe-name>/UsageTests/Misc.tests.cpp" >
@@ -20030,6 +20096,6 @@ loose text artifact
     </Section>
     <OverallResult success="true"/>
   </TestCase>
-  <OverallResults successes="1959" failures="146" expectedFailures="27"/>
+  <OverallResults successes="1965" failures="146" expectedFailures="27"/>
   <OverallResultsCases successes="280" failures="86" expectedFailures="7"/>
 </Catch2TestRun>

tests/SelfTest/IntrospectiveTests/CmdLine.tests.cpp

@@ -569,6 +569,27 @@ TEST_CASE( "Process can be configured on command line", "[config][command-line]"
             REQUIRE(config.benchmarkWarmupTime == 10);
         }
     }
+
+    SECTION("Sharding options") {
+        SECTION("shard-count") {
+            CHECK(cli.parse({ "test", "--shard-count=8"}));
+
+            REQUIRE(config.shardCount == 8);
+        }
+
+        SECTION("shard-index") {
+            CHECK(cli.parse({ "test", "--shard-index=2"}));
+
+            REQUIRE(config.shardIndex == 2);
+        }
+
+        SECTION("Zero shard-count") {
+            auto result = cli.parse({ "test", "--shard-count=0"});
+
+            CHECK( !result );
+            CHECK_THAT( result.errorMessage(), ContainsSubstring( "The shard count must be greater than 0" ) );
+        }
+    }
 }
 
 TEST_CASE("Test with special, characters \"in name", "[cli][regression]") {

tests/SelfTest/IntrospectiveTests/Sharding.tests.cpp

@@ -0,0 +1,41 @@
+/*
+ *  Distributed under the Boost Software License, Version 1.0. (See accompanying
+ *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/generators/catch_generators_all.hpp>
+
+#include <catch2/internal/catch_sharding.hpp>
+
+#include <unordered_map>
+#include <vector>
+
+TEST_CASE("Sharding Function", "[approvals]") {
+    std::vector<int> testContainer = { 0, 1, 2, 3, 4, 5, 6 };
+    std::unordered_map<int, std::vector<std::size_t>> expectedShardSizes = {
+        {1, {7}},
+        {2, {4, 3}},
+        {3, {3, 2, 2}},
+        {4, {2, 2, 2, 1}},
+        {5, {2, 2, 1, 1, 1}},
+        {6, {2, 1, 1, 1, 1, 1}},
+        {7, {1, 1, 1, 1, 1, 1, 1}},
+    };
+
+    auto shardCount = GENERATE(range(1, 7));
+    auto shardIndex = GENERATE_COPY(filter([=](int i) { return i < shardCount; }, range(0, 6)));
+
+    std::vector<int> result = Catch::createShard(testContainer, shardCount, shardIndex);
+
+    auto& sizes = expectedShardSizes[shardCount];
+    REQUIRE(result.size() == sizes[shardIndex]);
+
+    std::size_t startIndex = 0;
+    for(int i = 0; i < shardIndex; i++) {
+        startIndex += sizes[i];
+    }
+
+    for(std::size_t i = 0; i < sizes[shardIndex]; i++) {
+        CHECK(result[i] == testContainer[i + startIndex]);
+    }
+}

tests/TestScripts/testSharding.py

@@ -0,0 +1,90 @@
+#!/usr/bin/env python3
+
+"""
+This test script verifies that sharding tests does change which tests are run.
+This is done by running the binary multiple times, once to list all the tests,
+once per shard to list the tests for that shard, and once again per shard to
+execute the tests. The sharded lists are compared to the full list to ensure
+none are skipped, duplicated, and that the order remains the same. This process
+is repeated for multiple command line argument combinations to ensure sharding
+works with different filters and test orderings.
+"""
+
+import subprocess
+import sys
+import xml.etree.ElementTree as ET
+
+from collections import namedtuple
+
+def make_base_commandline(self_test_exe):
+    return [
+        self_test_exe,
+        '--reporter', 'xml',
+        "--shard-count", "5",
+        "--shard-index", "2",
+        "[generators]~[benchmarks]~[.]"
+    ]
+
+def list_tests(self_test_exe):
+    cmd = make_base_commandline(self_test_exe) + ['--list-tests']
+
+    process = subprocess.Popen(
+            cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    stdout, stderr = process.communicate()
+    if stderr:
+        raise RuntimeError("Unexpected error output:\n" + process.stderr)
+
+    root = ET.fromstring(stdout)
+    result = [elem.text for elem in root.findall('./TestCase/Name')]
+
+    if len(result) < 2:
+        raise RuntimeError("Unexpectedly few tests listed (got {})".format(
+            len(result)))
+
+    return result
+
+
+def execute_tests(self_test_exe):
+    cmd = make_base_commandline(self_test_exe)
+
+    process = subprocess.Popen(
+            cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    stdout, stderr = process.communicate()
+    if stderr:
+        raise RuntimeError("Unexpected error output:\n" + process.stderr)
+
+    root = ET.fromstring(stdout)
+    result = [elem.attrib["name"] for elem in root.findall('./TestCase')]
+
+    if len(result) < 2:
+        raise RuntimeError("Unexpectedly few tests listed (got {})".format(
+            len(result)))
+    return result
+
+
+def check_listed_and_executed_tests_match(listed_tests, executed_tests):
+        listed_names = set(listed_tests)
+        executed_names = set(executed_tests)
+
+        listed_string = "\n".join(listed_names)
+        exeucted_string = "\n".join(executed_names)
+
+        assert listed_names == executed_names, (
+            "Executed tests do not match the listed tests:\nExecuted:\n{}\n\nListed:\n{}".format(exeucted_string, listed_string)
+        )
+
+
+def test_sharding(self_test_exe):
+    listed_tests = list_tests(self_test_exe)
+    executed_tests = execute_tests(self_test_exe)
+
+    check_listed_and_executed_tests_match(listed_tests, executed_tests)
+
+
+def main():
+    self_test_exe, = sys.argv[1:]
+
+    test_sharding(self_test_exe)
+
+if __name__ == '__main__':
+    sys.exit(main())