diff --git a/crates/ptth_multi_call_server/src/main.rs b/crates/ptth_multi_call_server/src/main.rs
index 607d046..479453c 100644
--- a/crates/ptth_multi_call_server/src/main.rs
+++ b/crates/ptth_multi_call_server/src/main.rs
@@ -1,7 +1,9 @@
 use std::{
+	ffi::OsString,
 	iter::FromIterator,
 };
 
+#[derive (Debug, PartialEq)]
 enum Subcommand {
 	PtthServer,
 	PtthQuicEndServer,
@@ -22,30 +24,109 @@ fn parse_subcommand (name: &str) -> Option <Subcommand>
 	}
 }
 
+fn parse_args (args: &[OsString]) -> anyhow::Result <(Subcommand, &[OsString])>
+{
+	let arg_0 = match args.get (0) {
+		Some (x) => x,
+		None => anyhow::bail! ("arg 0 must be the exe name"),
+	};
+	
+	let arg_0 = arg_0.to_str ().ok_or_else (|| anyhow::anyhow! ("arg 0 should be valid UTF-8"))?;
+	match parse_subcommand (arg_0) {
+		Some (x) => return Ok ((x, args)),
+		None => (),
+	}
+	
+	let arg_1 = match args.get (1) {
+		Some (x) => x,
+		None => anyhow::bail! ("arg 1 must be the subcommand if arg 0 is not"),
+	};
+	
+	let arg_1 = arg_1.to_str ().ok_or_else (|| anyhow::anyhow! ("arg 1 subcommand should be valid UTF-8"))?;
+	match parse_subcommand (arg_1) {
+		Some (x) => return Ok ((x, &args [1..])),
+		None => (),
+	}
+	
+	anyhow::bail! ("Subcommand must be either arg 0 (exe name) or arg 1")
+}
+
 #[tokio::main]
 async fn main () -> anyhow::Result <()> {
 	tracing_subscriber::fmt::init ();
 	
 	let args = Vec::from_iter (std::env::args_os ());
 	
-	let arg_0 = args [0].to_str ().expect ("exe name should be valid UTF-8");
-	match parse_subcommand (arg_0) {
-		Some (Subcommand::PtthServer) => return ptth_server::executable::main (&args).await,
-		Some (Subcommand::PtthQuicEndServer) => return quic_demo::executable_end_server::main (&args).await,
-		_ => (),
+	let (subcommand, args) = parse_args (&args)?;
+	match subcommand {
+		Subcommand::PtthServer => ptth_server::executable::main (&args).await,
+		Subcommand::PtthQuicEndServer => quic_demo::executable_end_server::main (&args).await,
+	}
+}
+
+#[cfg (test)]
+mod tests {
+	use super::*;
+	
+	#[test]
+	fn multi_call () -> anyhow::Result <()> {
+		let negative_cases = vec! [
+			vec! [],
+			vec! ["invalid_exe_name"],
+			vec! ["ptth_multi_call_server"],
+			vec! ["ptth_multi_call_server", "invalid_subcommand"],
+		];
+		
+		for input in &negative_cases {
+			let input: Vec <_> = input.iter ().map (OsString::from).collect ();
+			
+			let actual = parse_args (&input);
+			assert! (actual.is_err ());
+		}
+		
+		let positive_cases = vec! [
+			(vec! ["ptth_server"], (Subcommand::PtthServer, vec! ["ptth_server"])),
+			(vec! ["ptth_server", "--help"], (Subcommand::PtthServer, vec! ["ptth_server", "--help"])),
+			(vec! ["ptth_quic_end_server", "--help"], (Subcommand::PtthQuicEndServer, vec! ["ptth_quic_end_server", "--help"])),
+			(vec! ["ptth_multi_call_server", "ptth_server"], (Subcommand::PtthServer, vec! ["ptth_server"])),
+			(
+				vec! [
+					"ptth_multi_call_server", 
+					"ptth_server", 
+					"--help"
+				], 
+				(
+					Subcommand::PtthServer, 
+					vec! [
+						"ptth_server", 
+						"--help"
+					]
+				)
+			),
+			(
+				vec! [
+					"invalid_exe_name", 
+					"ptth_server", 
+					"--help"
+				], 
+				(
+					Subcommand::PtthServer, 
+					vec! [
+						"ptth_server", 
+						"--help"
+					]
+				)
+			),
+		];
+		
+		for (input, (expected_subcommand, expected_args)) in &positive_cases {
+			let input: Vec <_> = input.iter ().map (OsString::from).collect ();
+			
+			let (actual_subcommand, actual_args) = parse_args (&input)?;
+			assert_eq! (expected_subcommand, &actual_subcommand);
+			assert_eq! (expected_args, actual_args);
+		}
+		
+		Ok (())
 	}
-	
-	let arg_1 = match args.get (1) {
-		Some (x) => x,
-		None => anyhow::bail! ("Subcommand must be the first argument if it's not the exe name"),
-	};
-	
-	let arg_1 = arg_1.to_str ().expect ("subcommand should be valid UTF-8");
-	match parse_subcommand (arg_1) {
-		Some (Subcommand::PtthServer) => return ptth_server::executable::main (&args [1..]).await,
-		Some (Subcommand::PtthQuicEndServer) => return quic_demo::executable_end_server::main (&args [1..]).await,
-		_ => (),
-	}
-	
-	anyhow::bail! ("Subcommand should be provided in exe name or first argument, e.g. `./ptth_multi_call_server ptth_server`");
 }