tests: Move run-pass tests without naming conflicts to ui

src/test/ui/string-box-error.rs

@@ -0,0 +1,12 @@
+// run-pass
+// Ensure that both `Box<dyn Error + Send + Sync>` and `Box<dyn Error>` can be
+// obtained from `String`.
+
+use std::error::Error;
+
+fn main() {
+    let _err1: Box<dyn Error + Send + Sync> = From::from("test".to_string());
+    let _err2: Box<dyn Error> = From::from("test".to_string());
+    let _err3: Box<dyn Error + Send + Sync + 'static> = From::from("test");
+    let _err4: Box<dyn Error> = From::from("test");
+}