projects/SelfTest/UsageTests/Generators.tests.cpp

#include "catch.hpp"

#include <cstring>


// Generators and sections can be nested freely
TEST_CASE("Generators -- simple", "[generators]") {
    auto i = GENERATE(1, 2, 3);
    SECTION("one") {
        auto j = GENERATE(values({ -3, -2, -1 }));
        REQUIRE(j < i);
    }

    SECTION("two") {
        // You can also explicitly set type for generators via Catch::Generators::as
        auto str = GENERATE(as<std::string>{}, "a", "bb", "ccc");
        REQUIRE(4u * i > str.size());
    }
}

// You can create a cartesian-product of generators by creating multiple ones
TEST_CASE("3x3x3 ints", "[generators]") {
    auto x = GENERATE(1, 2, 3);
    auto y = GENERATE(4, 5, 6);
    auto z = GENERATE(7, 8, 9);
    // These assertions will be run 27 times (3x3x3)
    CHECK(x < y);
    CHECK(y < z);
    REQUIRE(x < z);
}

// You can also create data tuples
TEST_CASE("tables", "[generators]") {
    // Note that this will not compile with libstdc++ older than libstdc++6
    // See https://stackoverflow.com/questions/12436586/tuple-vector-and-initializer-list
    // for possible workarounds
    //    auto data = GENERATE(table<char const*, int>({
    //        {"first", 5},
    //        {"second", 6},
    //        {"third", 5},
    //        {"etc...", 6}
    //    }));

    // Workaround for the libstdc++ bug mentioned above
    using tuple_type = std::tuple<char const*, int>;
    auto data = GENERATE(table<char const*, int>({
        tuple_type{"first", 5},
        tuple_type{"second", 6},
        tuple_type{"third", 5},
        tuple_type{"etc...", 6}
    }));

    REQUIRE(strlen(std::get<0>(data)) == static_cast<size_t>(std::get<1>(data)));
}


#ifdef __cpp_structured_bindings

// Structured bindings make the table utility much nicer to use
TEST_CASE( "strlen2", "[approvals][generators]" ) {
    auto [test_input, expected] = GENERATE( table<std::string, size_t>({
            {"one", 3},
            {"two", 3},
            {"three", 5},
            {"four", 4}
        }));

    REQUIRE( test_input.size() == expected );
}
#endif


// An alternate way of doing data tables without structured bindings
struct Data { std::string str; size_t len; };

TEST_CASE( "strlen3", "[generators]" ) {
    auto data = GENERATE( values<Data>({
            {"one", 3},
            {"two", 3},
            {"three", 5},
            {"four", 4}
        }));

    REQUIRE( data.str.size() == data.len );
}



#ifdef __cpp_structured_bindings

// Based on example from https://docs.cucumber.io/gherkin/reference/#scenario-outline
// (thanks to https://github.com/catchorg/Catch2/issues/850#issuecomment-399504851)

// Note that GIVEN, WHEN, and THEN now forward onto DYNAMIC_SECTION instead of SECTION.
// DYNAMIC_SECTION takes its name as a stringstream-style expression, so can be formatted using
// variables in scope - such as the generated variables here. This reads quite nicely in the
// test name output (the full scenario description).

static auto eatCucumbers( int start, int eat ) -> int { return start-eat; }

SCENARIO("Eating cucumbers", "[generators][approvals]") {

    auto [start, eat, left] = GENERATE( table<int,int,int> ({
            { 12, 5, 7 },
            { 20, 5, 15 }
        }));

    GIVEN( "there are " << start << " cucumbers" )
    WHEN( "I eat " << eat << " cucumbers" )
    THEN( "I should have " << left << " cucumbers" ) {
        REQUIRE( eatCucumbers( start, eat ) == left );
    }
}
#endif

// There are also some generic generator manipulators
TEST_CASE("Generators -- adapters", "[generators][generic]") {
    // TODO: This won't work yet, introduce GENERATE_VAR?
    //auto numbers = Catch::Generators::values({ 1, 2, 3, 4, 5, 6 });
    SECTION("Filtering by predicate") {
        SECTION("Basic usage") {
            // This filters out all odd (false) numbers, giving [2, 4, 6]
            auto i = GENERATE(filter([] (int val) { return val % 2 == 0; }, values({ 1, 2, 3, 4, 5, 6 })));
            REQUIRE(i % 2 == 0);
        }
        SECTION("Throws if there are no matching values") {
            using namespace Catch::Generators;
            REQUIRE_THROWS_AS(filter([] (int) {return false; }, value(1)), Catch::GeneratorException);
        }
    }
    SECTION("Shortening a range") {
        // This takes the first 3 elements from the values, giving back [1, 2, 3]
        auto i = GENERATE(take(3, values({ 1, 2, 3, 4, 5, 6 })));
        REQUIRE(i < 4);
    }
    SECTION("Transforming elements") {
        SECTION("Same type") {
            // This doubles values [1, 2, 3] into [2, 4, 6]
            auto i = GENERATE(map([] (int val) { return val * 2; }, values({ 1, 2, 3 })));
            REQUIRE(i % 2 == 0);
        }
        SECTION("Different type") {
            // This takes a generator that returns ints and maps them into strings
            auto i = GENERATE(map<std::string>([] (int val) { return std::to_string(val); }, values({ 1, 2, 3 })));
            REQUIRE(i.size() == 1);
        }
    }
    SECTION("Repeating a generator") {
        // This will return values [1, 2, 3, 1, 2, 3]
        auto j = GENERATE(repeat(2, values({ 1, 2, 3 })));
        REQUIRE(j > 0);
    }
    SECTION("Chunking a generator into sized pieces") {
        SECTION("Number of elements in source is divisible by chunk size") {
            auto chunk2 = GENERATE(chunk(2, values({ 1, 1, 2, 2, 3, 3 })));
            REQUIRE(chunk2.size() == 2);
            REQUIRE(chunk2.front() == chunk2.back());
        }
        SECTION("Number of elements in source is not divisible by chunk size") {
            auto chunk2 = GENERATE(chunk(2, values({ 1, 1, 2, 2, 3 })));
            REQUIRE(chunk2.size() == 2);
            REQUIRE(chunk2.front() == chunk2.back());
            REQUIRE(chunk2.front() < 3);
        }
        SECTION("Throws on too small generators") {
            using namespace Catch::Generators;
            REQUIRE_THROWS_AS(chunk(2, value(1)), Catch::GeneratorException);
        }
    }
}

// Note that because of the non-reproducibility of distributions,
// anything involving the random generators cannot be part of approvals
TEST_CASE("Random generator", "[generators][.][approvals]") {
    SECTION("Infer int from integral arguments") {
        auto val = GENERATE(take(4, random(0, 1)));
        STATIC_REQUIRE(std::is_same<decltype(val), int>::value);
        static_cast<void>(val); // Silence VS 2015 unused variable warning
    }
    SECTION("Infer double from double arguments") {
        auto val = GENERATE(take(4, random(0., 1.)));
        STATIC_REQUIRE(std::is_same<decltype(val), double>::value);
        static_cast<void>(val); // Silence VS 2015 unused variable warning
    }
}