test(derive): Ensure we don't break compatibility

tests/derive/legacy/app_name.rs

@@ -0,0 +1,97 @@
+use clap::CommandFactory;
+use clap::Parser;
+#[test]
+fn app_name_in_short_help_from_struct() {
+    #[derive(Parser)]
+    #[clap(name = "my-cmd")]
+    struct MyApp {}
+
+    let mut help = Vec::new();
+    MyApp::command().write_help(&mut help).unwrap();
+    let help = String::from_utf8(help).unwrap();
+
+    assert!(help.contains("my-cmd"));
+}
+
+#[test]
+fn app_name_in_long_help_from_struct() {
+    #[derive(Parser)]
+    #[clap(name = "my-cmd")]
+    struct MyApp {}
+
+    let mut help = Vec::new();
+    MyApp::command().write_long_help(&mut help).unwrap();
+    let help = String::from_utf8(help).unwrap();
+
+    assert!(help.contains("my-cmd"));
+}
+
+#[test]
+fn app_name_in_short_help_from_enum() {
+    #[derive(Parser)]
+    #[clap(name = "my-cmd")]
+    enum MyApp {}
+
+    let mut help = Vec::new();
+    MyApp::command().write_help(&mut help).unwrap();
+    let help = String::from_utf8(help).unwrap();
+
+    assert!(help.contains("my-cmd"));
+}
+
+#[test]
+fn app_name_in_long_help_from_enum() {
+    #[derive(Parser)]
+    #[clap(name = "my-cmd")]
+    enum MyApp {}
+
+    let mut help = Vec::new();
+    MyApp::command().write_long_help(&mut help).unwrap();
+    let help = String::from_utf8(help).unwrap();
+
+    assert!(help.contains("my-cmd"));
+}
+
+#[test]
+fn app_name_in_short_version_from_struct() {
+    #[derive(Parser)]
+    #[clap(name = "my-cmd")]
+    struct MyApp {}
+
+    let version = MyApp::command().render_version();
+
+    assert!(version.contains("my-cmd"));
+}
+
+#[test]
+fn app_name_in_long_version_from_struct() {
+    #[derive(Parser)]
+    #[clap(name = "my-cmd")]
+    struct MyApp {}
+
+    let version = MyApp::command().render_long_version();
+
+    assert!(version.contains("my-cmd"));
+}
+
+#[test]
+fn app_name_in_short_version_from_enum() {
+    #[derive(Parser)]
+    #[clap(name = "my-cmd")]
+    enum MyApp {}
+
+    let version = MyApp::command().render_version();
+
+    assert!(version.contains("my-cmd"));
+}
+
+#[test]
+fn app_name_in_long_version_from_enum() {
+    #[derive(Parser)]
+    #[clap(name = "my-cmd")]
+    enum MyApp {}
+
+    let version = MyApp::command().render_long_version();
+
+    assert!(version.contains("my-cmd"));
+}