C API: add nix_api_expr tests

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

@@ -0,0 +1,40 @@
+#pragma once
+///@file
+#include "tests/nix_api_util.hh"
+
+#include "nix_api_store.h"
+#include "nix_api_store_internal.h"
+
+#include <filesystem>
+#include <gtest/gtest.h>
+
+namespace fs = std::filesystem;
+
+class nix_api_store_test : public nix_api_util_context
+{
+public:
+    nix_api_store_test()
+    {
+        nix_libstore_init(ctx);
+
+        auto tmpl = nix::getEnv("TMPDIR").value_or("/tmp") + "/tests_nix-store.XXXXXX";
+        nixStoreDir = mkdtemp((char *) tmpl.c_str());
+
+        // Options documented in `nix help-stores`
+        const char * p1[] = {"root", nixStoreDir.c_str()};
+        const char ** params[] = {p1, nullptr};
+        store = nix_store_open(ctx, "local", params);
+    };
+    ~nix_api_store_test() override
+    {
+        nix_store_unref(store);
+
+        for (auto & path : fs::recursive_directory_iterator(nixStoreDir)) {
+            fs::permissions(path, fs::perms::owner_all);
+        }
+        fs::remove_all(nixStoreDir);
+    }
+
+    Store * store;
+    std::string nixStoreDir;
+};