Add tests for new specializations of Merge()

Author: nbusser

src/ftxui/dom/hbox_test.cpp

@@ -2,9 +2,12 @@
 // Use of this source code is governed by the MIT license that can be found in
 // the LICENSE file.
 #include <gtest/gtest.h>  // for Test, TestInfo (ptr only), EXPECT_EQ, Message, TEST, TestPartResult
-#include <cstddef>  // for size_t
-#include <string>   // for allocator, basic_string, string
-#include <vector>   // for vector
+#include <array>          // for array
+#include <cstddef>        // for size_t
+#include <stack>          // for stack
+#include <string>         // for allocator, basic_string, string
+#include <unordered_set>  // for unordered_set
+#include <vector>         // for vector
 
 #include "ftxui/dom/elements.hpp"  // for text, operator|, Element, flex_grow, flex_shrink, hbox
 #include "ftxui/dom/node.hpp"       // for Render
@@ -358,5 +361,39 @@ TEST(HBoxTest, FlexGrow_NoFlex_FlewShrink) {
   }
 }
 
+TEST(HBoxTest, FromElementsContainer) {
+  Elements elements_vector{text("0"), text("1")};
+
+  std::array<Element, 2> elements_array{text("0"), text("1")};
+
+  std::deque<Element> elements_deque{text("0"), text("1")};
+
+  std::stack<Element> elements_stack;
+  elements_stack.push(text("1"));
+  elements_stack.push(text("0"));
+
+  std::queue<Element> elements_queue;
+  elements_queue.emplace(text("0"));
+  elements_queue.emplace(text("1"));
+
+  const std::vector<Element> collection_hboxes{
+      hbox(std::move(elements_vector)), hbox(std::move(elements_array)),
+      hbox(std::move(elements_stack)),  hbox(std::move(elements_deque)),
+      hbox(std::move(elements_queue)),
+  };
+
+  for (const Element& collection_hbox : collection_hboxes) {
+    Screen screen(2, 1);
+    Render(screen, collection_hbox);
+    EXPECT_EQ("01", screen.ToString());
+  }
+
+  // Exception: unordered set, which has no guaranteed order.
+  std::unordered_set<Element> elements_set{text("0"), text("0")};
+  Screen screen(2, 1);
+  Render(screen, hbox(elements_set));
+  EXPECT_EQ("00", screen.ToString());
+};
+
 }  // namespace ftxui
 // NOLINTEND