Add config subcommand to validate configuration

codex-rs/cli/tests/config.rs

@@ -0,0 +1,44 @@
+use std::fs;
+use std::path::Path;
+
+use anyhow::Result;
+use assert_cmd::Command;
+use tempfile::TempDir;
+
+fn codex_command(codex_home: &Path) -> Result<Command> {
+    let mut cmd = Command::cargo_bin("codex")?;
+    cmd.env("CODEX_HOME", codex_home);
+    Ok(cmd)
+}
+
+#[test]
+fn config_subcommand_reports_success_for_valid_config() -> Result<()> {
+    let codex_home = TempDir::new()?;
+    let config_path = codex_home.path().join("config.toml");
+    fs::write(config_path, "model = \"gpt-5\"\n")?;
+
+    let mut cmd = codex_command(codex_home.path())?;
+    let output = cmd.arg("config").output()?;
+
+    assert!(output.status.success());
+    let stdout = String::from_utf8(output.stdout)?;
+    assert!(stdout.contains("Configuration validated successfully"));
+
+    Ok(())
+}
+
+#[test]
+fn config_subcommand_exits_with_code_three_on_validation_error() -> Result<()> {
+    let codex_home = TempDir::new()?;
+    let config_path = codex_home.path().join("config.toml");
+    fs::write(config_path, "model = 123\n")?;
+
+    let mut cmd = codex_command(codex_home.path())?;
+    let output = cmd.arg("config").output()?;
+
+    assert_eq!(output.status.code(), Some(3));
+    let stderr = String::from_utf8(output.stderr)?;
+    assert!(stderr.contains("Config validation error"));
+
+    Ok(())
+}