Move unit tests to the location Meson expects them to be

Everything that is a separate subproject should live in the subprojects
directory.

Progress on #2503

This reverts commit 451f8a8c19.

src/libstore-test-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
+{
+    std::filesystem::path unitTestData = getUnitTestData() / protocolDir;
+
+    std::filesystem::path goldenMaster(std::string_view testStem) const override {
+        return unitTestData / (std::string { 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); \
+    }
+
+}