Now have more test for the base functionality but need to push render tests and find a way to test the GUI. I've also brought in sol2 for lua integration but not sure what to do with it.

tests/panel.cpp

@@ -0,0 +1,75 @@
+#include <catch2/catch_test_macros.hpp>
+#include <fmt/core.h>
+#include <ftxui/screen/terminal.hpp>  // for ColorSupport, Color, Palette16, Palette256, TrueColor
+#include <ftxui/dom/elements.hpp>  // for hflow, paragraph, separator, hbox, vbox, filler, operator|, border, Element
+#include "panel.hpp"
+#include "ansi_parser.hpp"
+
+using namespace ftxui;
+using namespace fmt;
+using std::string;
+
+void test_ansi_parsing(Panel &panel) {
+  sf::Color default_fg(0,0,0);
+  sf::Color default_bg(100,100,100);
+  // this sets the Truecolor so need to do it first
+  ANSIParser ansi(default_fg, default_bg);
+
+  bool good = ansi.parse(panel.to_string(),
+    [&](sf::Color color, sf::Color bgcolor){
+      // ignore color
+    },
+    [&](wchar_t ch) {
+      // ignore char
+  });
+
+  REQUIRE(good == true);
+}
+
+TEST_CASE("can render a simple text panel", "[panel]") {
+  ftxui::Terminal::SetColorSupport(ftxui::Terminal::Color::TrueColor);
+
+  Panel text_panel(0, 0, 20, 5);
+
+  bool show_modal = false;
+
+  auto buttons = Container::Horizontal({
+      Button("OK", [&]{ show_modal = false; }),
+      Button("CANCEL", [&]{ show_modal = false; }),
+  });
+
+  auto text_box = Renderer([buttons]{
+      return hbox({
+        hflow(
+            vbox(text("I AM TEXT")),
+            buttons->Render()
+        )});
+    });
+
+  text_panel.set_renderer(text_box);
+  text_panel.add(buttons);
+
+  text_panel.resize(10,10);
+  text_panel.render();
+  test_ansi_parsing(text_panel);
+
+  const Screen &screen = text_panel.screen();
+  REQUIRE(screen.dimx() == 10);
+  REQUIRE(screen.dimx() == 10);
+}
+
+TEST_CASE("can render a simple grid panel", "[panel]") {
+  Terminal::SetColorSupport(Terminal::Color::TrueColor);
+
+  Panel grid_panel(20, 20, 20, 5, true);
+
+  auto text_box = Renderer([]{
+      return hbox({
+        hflow(vbox(text("I AM TEXT")))});
+    });
+
+  grid_panel.set_renderer(text_box);
+  grid_panel.resize(10,10);
+  grid_panel.render();
+  test_ansi_parsing(grid_panel);
+}