Move tests next to their implementations.

src/ftxui/dom/gauge_test.cpp

@@ -0,0 +1,31 @@
+#include "ftxui/dom/elements.hpp"
+#include "ftxui/screen/screen.hpp"
+#include "gtest/gtest.h"
+
+using namespace ftxui;
+using namespace ftxui;
+
+TEST(GaugeTest, zero) {
+  auto root = gauge(0);
+  Screen screen(11, 1);
+  Render(screen, root.get());
+
+  EXPECT_EQ("           ", screen.ToString());
+}
+
+TEST(GaugeTest, half) {
+  auto root = gauge(0.5);
+  Screen screen(11, 1);
+  Render(screen, root.get());
+
+  EXPECT_EQ("█████▍     ", screen.ToString());
+  //"  ▏▎▍▌▊▉█";
+}
+
+TEST(GaugeTest, one) {
+  auto root = gauge(1.0);
+  Screen screen(11, 1);
+  Render(screen, root.get());
+
+  EXPECT_EQ("███████████", screen.ToString());
+}