add newly created Linux files

linux/polyvox_filament_plugin_private.h

@@ -0,0 +1,10 @@
+#include <flutter_linux/flutter_linux.h>
+
+#include "include/polyvox_filament/polyvox_filament_plugin.h"
+
+// This file exposes some plugin internals for unit testing. See
+// https://github.com/flutter/flutter/issues/88724 for current limitations
+// in the unit-testable API.
+
+// Handles the getPlatformVersion method call.
+FlMethodResponse *get_platform_version();

linux/test/polyvox_filament_plugin_test.cc

@@ -0,0 +1,31 @@
+#include <flutter_linux/flutter_linux.h>
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+#include "include/polyvox_filament/polyvox_filament_plugin.h"
+#include "polyvox_filament_plugin_private.h"
+
+// This demonstrates a simple unit test of the C portion of this plugin's
+// implementation.
+//
+// Once you have built the plugin's example app, you can run these tests
+// from the command line. For instance, for a plugin called my_plugin
+// built for x64 debug, run:
+// $ build/linux/x64/debug/plugins/my_plugin/my_plugin_test
+
+namespace polyvox_filament {
+namespace test {
+
+TEST(PolyvoxFilamentPlugin, GetPlatformVersion) {
+  g_autoptr(FlMethodResponse) response = get_platform_version();
+  ASSERT_NE(response, nullptr);
+  ASSERT_TRUE(FL_IS_METHOD_SUCCESS_RESPONSE(response));
+  FlValue* result = fl_method_success_response_get_result(
+      FL_METHOD_SUCCESS_RESPONSE(response));
+  ASSERT_EQ(fl_value_get_type(result), FL_VALUE_TYPE_STRING);
+  // The full string varies, so just validate that it has the right format.
+  EXPECT_THAT(fl_value_get_string(result), testing::StartsWith("Linux "));
+}
+
+}  // namespace test
+}  // namespace polyvox_filament