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/nix_api_store.hh

@@ -0,0 +1,73 @@
+#pragma once
+///@file
+#include "tests/nix_api_util.hh"
+
+#include "file-system.hh"
+#include <filesystem>
+
+#include "nix_api_store.h"
+#include "nix_api_store_internal.h"
+
+#include <filesystem>
+#include <gtest/gtest.h>
+
+namespace fs { using namespace std::filesystem; }
+
+namespace nixC {
+class nix_api_store_test : public nix_api_util_context
+{
+public:
+    nix_api_store_test()
+    {
+        nix_libstore_init(ctx);
+        init_local_store();
+    };
+
+    ~nix_api_store_test() override
+    {
+        nix_store_free(store);
+
+        for (auto & path : fs::recursive_directory_iterator(nixDir)) {
+            fs::permissions(path, fs::perms::owner_all);
+        }
+        fs::remove_all(nixDir);
+    }
+
+    Store * store;
+    std::string nixDir;
+    std::string nixStoreDir;
+
+protected:
+    void init_local_store()
+    {
+#ifdef _WIN32
+        // no `mkdtemp` with MinGW
+        auto tmpl = nix::defaultTempDir() + "/tests_nix-store.";
+        for (size_t i = 0; true; ++i) {
+            nixDir = tmpl + std::string { i };
+            if (fs::create_directory(nixDir)) break;
+        }
+#else
+        // resolve any symlinks in i.e. on macOS /tmp -> /private/tmp
+        // because this is not allowed for a nix store.
+        auto tmpl = nix::absPath(std::filesystem::path(nix::defaultTempDir()) / "tests_nix-store.XXXXXX", true);
+        nixDir = mkdtemp((char *) tmpl.c_str());
+#endif
+
+        nixStoreDir = nixDir + "/my_nix_store";
+
+        // Options documented in `nix help-stores`
+        const char * p1[] = {"store", nixStoreDir.c_str()};
+        const char * p2[] = {"state", (new std::string(nixDir + "/my_state"))->c_str()};
+        const char * p3[] = {"log", (new std::string(nixDir + "/my_log"))->c_str()};
+
+        const char ** params[] = {p1, p2, p3, nullptr};
+
+        store = nix_store_open(ctx, "local", params);
+        if (!store) {
+            std::string errMsg = nix_err_msg(nullptr, ctx, nullptr);
+            ASSERT_NE(store, nullptr) << "Could not open store: " << errMsg;
+        };
+    }
+};
+}