Passed test for multiline help message alignment

test/test_help.cpp

@@ -1,6 +1,8 @@
 #include <argparse/argparse.hpp>
 #include <doctest.hpp>
+#include <regex>
 #include <sstream>
+#include <unordered_map>
 
 using doctest::test_suite;
 
@@ -73,3 +75,57 @@ TEST_CASE("Users can replace default -h/--help" * test_suite("help")) {
   program.parse_args({"test", "--help"});
   REQUIRE_FALSE(buffer.str().empty());
 }
+
+TEST_CASE("Multiline help message alignment") {
+  argparse::ArgumentParser program("program");
+  program.add_argument("input1")
+      .help(
+        "This is the first line of help message.\n"
+        "And this is the second line of help message."
+      );
+  program.add_argument("program_input2")
+      .help("There is only one line.");
+  program.add_argument("-p", "--prog_input3")
+      .help(
+R"(Lorem ipsum dolor sit amet, consectetur adipiscing elit.
+Sed ut perspiciatis unde omnis iste natus error sit voluptatem
+accusantium doloremque laudantium, totam rem aperiam...)"
+      );
+
+  std::ostringstream stream;
+  stream << program;
+  std::string help_text = stream.str();
+
+  // Split the help text into lines
+  std::istringstream iss(help_text);
+  std::vector<std::string> help_lines;
+  std::string line;
+  while (std::getline(iss, line)) {
+    help_lines.push_back(line);
+  }
+
+  // A map to store the starting position of the help text for each argument
+  std::unordered_map<std::string, int> help_start_positions;
+
+  for (const auto& line : help_lines) {
+    // Find the argument names in the line
+    std::smatch match;
+    if (std::regex_search(line, match, std::regex(R"((input1|program_input2|--prog_input3))"))) {
+      std::string arg_name = match.str();
+
+      // Find the position of the first non-space character after the argument name
+      int position = line.find_first_not_of(' ', match.position() + arg_name.size());
+      if (position == std::string::npos) {
+        continue;
+      }
+      help_start_positions[arg_name] = position;
+    }
+  }
+
+  // Check if the positions are the same for all arguments
+  REQUIRE(!help_start_positions.empty());
+  int first_position = help_start_positions.begin()->second;
+  for (const auto& entry : help_start_positions) {
+    REQUIRE(entry.second == first_position);
+  }
+}