Add test verifying diagnostic

tests/test_diagnostic_source_macro.rs

@@ -1,5 +1,16 @@
 use miette::Diagnostic;
 
+#[derive(Debug, miette::Diagnostic, thiserror::Error)]
+#[error("A complex error happened")]
+struct SourceError {
+    #[source_code]
+    code: String,
+    #[help]
+    help: String,
+    #[label("here")]
+    label: (usize, usize),
+}
+
 #[derive(Debug, miette::Diagnostic, thiserror::Error)]
 #[error("AnErr")]
 struct AnErr;
@@ -59,3 +70,34 @@ fn test_diagnostic_source() {
     let error = TestArcedError(std::sync::Arc::new(AnErr));
     assert!(error.diagnostic_source().is_some());
 }
+
+#[test]
+fn test_diagnostic_source_pass_extra_info() {
+    let diag = TestBoxedError(Box::new(SourceError {
+        code: String::from("Hello\nWorld!"),
+        help: format!("Have you tried turning it on and off again?"),
+        label: (1, 4),
+    }));
+    let mut out = String::new();
+    miette::GraphicalReportHandler::new_themed(miette::GraphicalTheme::unicode_nocolor())
+        .with_width(80)
+        .with_footer("this is a footer".into())
+        .render_report(&mut out, &diag)
+        .unwrap();
+    println!("Error: {}", out);
+    let expected = r#"  × TestError
+  ╰─▶   × A complex error happened
+         ╭─[1:1]
+       1 │ Hello
+         ·  ──┬─
+         ·    ╰── here
+       2 │ World!
+         ╰────
+        help: Have you tried turning it on and off again?
+      
+
+  this is a footer
+"#
+    .to_string();
+    assert_eq!(expected, out);
+}