Adds UI widget tests

Adds unit tests for UI components.
UI_can, UI_stacked_widget, UI_status_bar and UI_tab_widget

tests/UI_status_bar.cpp

@@ -0,0 +1,22 @@
+#include "Test.hpp"
+
+TEST(UI_status_bar, to_from_json)
+{
+    UI_status_bar statusbar("message");
+    json j = statusbar.to_json(0);
+    UI_status_bar statusbar2;
+    statusbar2.from_json(j);
+    EXPECT_EQ(statusbar.text(), statusbar2.text());
+}
+
+TEST(UI_status_bar, show_message)
+{
+    UI_status_bar statusbar("message");
+    QSignalSpy spy_ui(&statusbar, &UI_status_bar::ui_changed);
+    EXPECT_EQ(statusbar.text(), "message");
+    EXPECT_EQ(statusbar.timeout(), 0);
+    statusbar.show_message("random text", 3);
+    EXPECT_EQ(statusbar.text(), "random text");
+    EXPECT_EQ(statusbar.timeout(), 3);
+    EXPECT_EQ(spy_ui.count(), 1);
+}