Separate internal from non-internal unit tests of the C API

This helps us make sure that the external C API is sufficient for the
tasks that we think it is sufficient for.

src/libutil-tests/nix_api_util_internal.cc

@@ -0,0 +1,85 @@
+#include "nix/util/config-global.hh"
+#include "nix/util/args.hh"
+#include "nix_api_util.h"
+#include "nix_api_util_internal.h"
+#include "nix/util/tests/nix_api_util.hh"
+#include "nix/util/tests/string_callback.hh"
+
+#include <gtest/gtest.h>
+
+#include <memory>
+
+#include "util-tests-config.hh"
+
+namespace nixC {
+
+TEST_F(nix_api_util_context, nix_context_error)
+{
+    std::string err_msg_ref;
+    try {
+        throw nix::Error("testing error");
+    } catch (nix::Error & e) {
+        err_msg_ref = e.what();
+        nix_context_error(ctx);
+    }
+    ASSERT_EQ(nix_err_code(ctx), NIX_ERR_NIX_ERROR);
+    ASSERT_EQ(ctx->name, "nix::Error");
+    ASSERT_EQ(*ctx->last_err, err_msg_ref);
+    ASSERT_EQ(ctx->info->msg.str(), "testing error");
+
+    try {
+        throw std::runtime_error("testing exception");
+    } catch (std::exception & e) {
+        err_msg_ref = e.what();
+        nix_context_error(ctx);
+    }
+    ASSERT_EQ(nix_err_code(ctx), NIX_ERR_UNKNOWN);
+    ASSERT_EQ(*ctx->last_err, err_msg_ref);
+
+    nix_clear_err(ctx);
+    ASSERT_EQ(nix_err_code(ctx), NIX_OK);
+}
+
+TEST_F(nix_api_util_context, nix_set_err_msg)
+{
+    ASSERT_EQ(nix_err_code(ctx), NIX_OK);
+    nix_set_err_msg(ctx, NIX_ERR_UNKNOWN, "unknown test error");
+    ASSERT_EQ(nix_err_code(ctx), NIX_ERR_UNKNOWN);
+    ASSERT_EQ(*ctx->last_err, "unknown test error");
+}
+
+TEST_F(nix_api_util_context, nix_err_info_msg)
+{
+    std::string err_info;
+
+    // no error
+    EXPECT_THROW(nix_err_info_msg(NULL, ctx, OBSERVE_STRING(err_info)), nix::Error);
+
+    try {
+        throw nix::Error("testing error");
+    } catch (...) {
+        nix_context_error(ctx);
+    }
+    auto new_ctx = createOwnedNixContext();
+    nix_err_info_msg(new_ctx.get(), ctx, OBSERVE_STRING(err_info));
+    ASSERT_STREQ("testing error", err_info.c_str());
+}
+
+TEST_F(nix_api_util_context, nix_err_name)
+{
+    std::string err_name;
+
+    // no error
+    EXPECT_THROW(nix_err_name(NULL, ctx, OBSERVE_STRING(err_name)), nix::Error);
+
+    try {
+        throw nix::Error("testing error");
+    } catch (...) {
+        nix_context_error(ctx);
+    }
+    auto new_ctx = createOwnedNixContext();
+    nix_err_name(new_ctx.get(), ctx, OBSERVE_STRING(err_name));
+    ASSERT_EQ(std::string(err_name), "nix::Error");
+}
+
+} // namespace nixC