test: rework lib stuff to share common files

test/lib/emitter/plugin/main.cpp

@@ -0,0 +1,28 @@
+#define CR_HOST
+
+#include <gtest/gtest.h>
+#include <cr.h>
+#include "types.h"
+
+TEST(Lib, Emitter) {
+    test_emitter emitter;
+    int value{};
+
+    ASSERT_EQ(value, 0);
+
+    emitter.on<message>([&](message msg, test_emitter &owner) {
+        value = msg.payload;
+        owner.erase<message>();
+    });
+
+    cr_plugin ctx;
+    cr_plugin_load(ctx, PLUGIN);
+
+    ctx.userdata = &emitter;
+    cr_plugin_update(ctx);
+
+    ASSERT_EQ(value, 42);
+
+    emitter = {};
+    cr_plugin_close(ctx);
+}