Move tests to separate directories, and document

Today, with the tests inside a `tests` intermingled with the
corresponding library's source code, we have a few problems:

- We have to be careful that wildcards don't end up with tests being
  built as part of Nix proper, or test headers being installed as part
  of Nix proper.

- Tests in libraries but not executables is not right:

  - It means each executable runs the previous unit tests again, because
    it needs the libraries.

  - It doesn't work right on Windows, which doesn't want you to load a
    DLL just for the side global variable . It could be made to work
    with the dlopen equivalent, but that's gross!

This reorg solves these problems.

There is a remaining problem which is that sibbling headers (like
`hash.hh` the test header vs `hash.hh` the main `libnixutil` header) end
up shadowing each other. This PR doesn't solve that. That is left as
future work for a future PR.

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>

tests/unit/libstore-support/tests/derived-path.cc

@@ -0,0 +1,57 @@
+#include <regex>
+
+#include <rapidcheck.h>
+
+#include "tests/derived-path.hh"
+
+namespace rc {
+using namespace nix;
+
+Gen<DerivedPath::Opaque> Arbitrary<DerivedPath::Opaque>::arbitrary()
+{
+    return gen::just(DerivedPath::Opaque {
+        .path = *gen::arbitrary<StorePath>(),
+    });
+}
+
+Gen<SingleDerivedPath::Built> Arbitrary<SingleDerivedPath::Built>::arbitrary()
+{
+    return gen::just(SingleDerivedPath::Built {
+        .drvPath = make_ref<SingleDerivedPath>(*gen::arbitrary<SingleDerivedPath>()),
+        .output = (*gen::arbitrary<StorePathName>()).name,
+    });
+}
+
+Gen<DerivedPath::Built> Arbitrary<DerivedPath::Built>::arbitrary()
+{
+    return gen::just(DerivedPath::Built {
+        .drvPath = make_ref<SingleDerivedPath>(*gen::arbitrary<SingleDerivedPath>()),
+        .outputs = *gen::arbitrary<OutputsSpec>(),
+    });
+}
+
+Gen<SingleDerivedPath> Arbitrary<SingleDerivedPath>::arbitrary()
+{
+    switch (*gen::inRange<uint8_t>(0, std::variant_size_v<SingleDerivedPath::Raw>)) {
+    case 0:
+        return gen::just<SingleDerivedPath>(*gen::arbitrary<SingleDerivedPath::Opaque>());
+    case 1:
+        return gen::just<SingleDerivedPath>(*gen::arbitrary<SingleDerivedPath::Built>());
+    default:
+        assert(false);
+    }
+}
+
+Gen<DerivedPath> Arbitrary<DerivedPath>::arbitrary()
+{
+    switch (*gen::inRange<uint8_t>(0, std::variant_size_v<DerivedPath::Raw>)) {
+    case 0:
+        return gen::just<DerivedPath>(*gen::arbitrary<DerivedPath::Opaque>());
+    case 1:
+        return gen::just<DerivedPath>(*gen::arbitrary<DerivedPath::Built>());
+    default:
+        assert(false);
+    }
+}
+
+}

tests/unit/libstore-support/tests/derived-path.hh

@@ -0,0 +1,39 @@
+#pragma once
+///@file
+
+#include <rapidcheck/gen/Arbitrary.h>
+
+#include <derived-path.hh>
+
+#include "tests/path.hh"
+#include "tests/outputs-spec.hh"
+
+namespace rc {
+using namespace nix;
+
+template<>
+struct Arbitrary<SingleDerivedPath::Opaque> {
+    static Gen<SingleDerivedPath::Opaque> arbitrary();
+};
+
+template<>
+struct Arbitrary<SingleDerivedPath::Built> {
+    static Gen<SingleDerivedPath::Built> arbitrary();
+};
+
+template<>
+struct Arbitrary<SingleDerivedPath> {
+    static Gen<SingleDerivedPath> arbitrary();
+};
+
+template<>
+struct Arbitrary<DerivedPath::Built> {
+    static Gen<DerivedPath::Built> arbitrary();
+};
+
+template<>
+struct Arbitrary<DerivedPath> {
+    static Gen<DerivedPath> arbitrary();
+};
+
+}

tests/unit/libstore-support/tests/libstore.hh

@@ -0,0 +1,26 @@
+#pragma once
+///@file
+
+#include <gtest/gtest.h>
+#include <gmock/gmock.h>
+
+#include "store-api.hh"
+
+namespace nix {
+
+class LibStoreTest : public virtual ::testing::Test {
+    public:
+        static void SetUpTestSuite() {
+            initLibStore();
+        }
+
+    protected:
+        LibStoreTest()
+            : store(openStore("dummy://"))
+        { }
+
+        ref<Store> store;
+};
+
+
+} /* namespace nix */

tests/unit/libstore-support/tests/outputs-spec.cc

@@ -0,0 +1,24 @@
+#include "tests/outputs-spec.hh"
+
+#include <rapidcheck.h>
+
+namespace rc {
+using namespace nix;
+
+Gen<OutputsSpec> Arbitrary<OutputsSpec>::arbitrary()
+{
+    switch (*gen::inRange<uint8_t>(0, std::variant_size_v<OutputsSpec::Raw>)) {
+    case 0:
+        return gen::just((OutputsSpec) OutputsSpec::All { });
+    case 1:
+        return gen::just((OutputsSpec) OutputsSpec::Names {
+            *gen::nonEmpty(gen::container<StringSet>(gen::map(
+                gen::arbitrary<StorePathName>(),
+                [](StorePathName n) { return n.name; }))),
+        });
+    default:
+        assert(false);
+    }
+}
+
+}

tests/unit/libstore-support/tests/outputs-spec.hh

@@ -0,0 +1,18 @@
+#pragma once
+///@file
+
+#include <rapidcheck/gen/Arbitrary.h>
+
+#include <outputs-spec.hh>
+
+#include "tests/path.hh"
+
+namespace rc {
+using namespace nix;
+
+template<>
+struct Arbitrary<OutputsSpec> {
+    static Gen<OutputsSpec> arbitrary();
+};
+
+}

tests/unit/libstore-support/tests/path.cc

@@ -0,0 +1,82 @@
+#include <regex>
+
+#include <rapidcheck.h>
+
+#include "path-regex.hh"
+#include "store-api.hh"
+
+#include "tests/hash.hh"
+#include "tests/path.hh"
+
+namespace nix {
+
+void showValue(const StorePath & p, std::ostream & os)
+{
+    os << p.to_string();
+}
+
+}
+
+namespace rc {
+using namespace nix;
+
+Gen<StorePathName> Arbitrary<StorePathName>::arbitrary()
+{
+    auto len = *gen::inRange<size_t>(
+        1,
+        StorePath::MaxPathLen - StorePath::HashLen);
+
+    std::string pre;
+    pre.reserve(len);
+
+    for (size_t c = 0; c < len; ++c) {
+        switch (auto i = *gen::inRange<uint8_t>(0, 10 + 2 * 26 + 6)) {
+            case 0 ... 9:
+                pre += '0' + i;
+            case 10 ... 35:
+                pre += 'A' + (i - 10);
+                break;
+            case 36 ... 61:
+                pre += 'a' + (i - 36);
+                break;
+            case 62:
+                pre += '+';
+                break;
+            case 63:
+                pre += '-';
+                break;
+            case 64:
+                // names aren't permitted to start with a period,
+                // so just fall through to the next case here
+                if (c != 0) {
+                    pre += '.';
+                    break;
+                }
+            case 65:
+                pre += '_';
+                break;
+            case 66:
+                pre += '?';
+                break;
+            case 67:
+                pre += '=';
+                break;
+            default:
+                assert(false);
+        }
+    }
+
+    return gen::just(StorePathName {
+        .name = std::move(pre),
+    });
+}
+
+Gen<StorePath> Arbitrary<StorePath>::arbitrary()
+{
+    return gen::just(StorePath {
+        *gen::arbitrary<Hash>(),
+        (*gen::arbitrary<StorePathName>()).name,
+    });
+}
+
+} // namespace rc

tests/unit/libstore-support/tests/path.hh

@@ -0,0 +1,32 @@
+#pragma once
+///@file
+
+#include <rapidcheck/gen/Arbitrary.h>
+
+#include <path.hh>
+
+namespace nix {
+
+struct StorePathName {
+    std::string name;
+};
+
+// For rapidcheck
+void showValue(const StorePath & p, std::ostream & os);
+
+}
+
+namespace rc {
+using namespace nix;
+
+template<>
+struct Arbitrary<StorePathName> {
+    static Gen<StorePathName> arbitrary();
+};
+
+template<>
+struct Arbitrary<StorePath> {
+    static Gen<StorePath> arbitrary();
+};
+
+}

tests/unit/libstore-support/tests/protocol.hh

@@ -0,0 +1,75 @@
+#pragma once
+///@file
+
+#include <nlohmann/json.hpp>
+#include <gtest/gtest.h>
+
+#include "tests/libstore.hh"
+#include "tests/characterization.hh"
+
+namespace nix {
+
+template<class Proto, const char * protocolDir>
+class ProtoTest : public CharacterizationTest, public LibStoreTest
+{
+    Path unitTestData = getUnitTestData() + "/" + protocolDir;
+
+    Path goldenMaster(std::string_view testStem) const override {
+        return unitTestData + "/" + testStem + ".bin";
+    }
+};
+
+template<class Proto, const char * protocolDir>
+class VersionedProtoTest : public ProtoTest<Proto, protocolDir>
+{
+public:
+    /**
+     * Golden test for `T` reading
+     */
+    template<typename T>
+    void readProtoTest(PathView testStem, typename Proto::Version version, T expected)
+    {
+        CharacterizationTest::readTest(testStem, [&](const auto & encoded) {
+            T got = ({
+                StringSource from { encoded };
+                Proto::template Serialise<T>::read(
+                    *LibStoreTest::store,
+                    typename Proto::ReadConn {
+                        .from = from,
+                        .version = version,
+                    });
+            });
+
+            ASSERT_EQ(got, expected);
+        });
+    }
+
+    /**
+     * Golden test for `T` write
+     */
+    template<typename T>
+    void writeProtoTest(PathView testStem, typename Proto::Version version, const T & decoded)
+    {
+        CharacterizationTest::writeTest(testStem, [&]() {
+            StringSink to;
+            Proto::template Serialise<T>::write(
+                *LibStoreTest::store,
+                typename Proto::WriteConn {
+                    .to = to,
+                    .version = version,
+                },
+                decoded);
+            return std::move(to.s);
+        });
+    }
+};
+
+#define VERSIONED_CHARACTERIZATION_TEST(FIXTURE, NAME, STEM, VERSION, VALUE) \
+    TEST_F(FIXTURE, NAME ## _read) { \
+        readProtoTest(STEM, VERSION, VALUE); \
+    } \
+    TEST_F(FIXTURE, NAME ## _write) { \
+        writeProtoTest(STEM, VERSION, VALUE); \
+    }
+
+}