Move std::error unit tests to integration tests

Author: bjorn3

std/src/error.rs

@@ -1,9 +1,6 @@
 #![doc = include_str!("../../core/src/error.md")]
 #![stable(feature = "rust1", since = "1.0.0")]
 
-#[cfg(test)]
-mod tests;
-
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::error::Error;
 #[unstable(feature = "error_generic_member_access", issue = "99301")]

std/src/error/tests.rs std/tests/error.rs

@@ -1,7 +1,8 @@
-use core::error::Request;
+#![feature(error_generic_member_access, error_reporter)]
 
-use super::Error;
-use crate::fmt;
+use std::backtrace::Backtrace;
+use std::error::{Error, Report, Request};
+use std::fmt;
 
 #[derive(Debug, PartialEq)]
 struct A;
@@ -38,9 +39,6 @@ fn downcasting() {
     }
 }
 
-use crate::backtrace::Backtrace;
-use crate::error::Report;
-
 #[derive(Debug)]
 struct SuperError {
     source: SuperErrorSideKick,