diff --git a/tests/ui/error-codes/E0259.rs b/tests/ui/error-codes/E0259.rs
index e7e94d58635..78e56deccb4 100644
--- a/tests/ui/error-codes/E0259.rs
+++ b/tests/ui/error-codes/E0259.rs
@@ -1,8 +1,8 @@
-#![feature(rustc_private)]
+#![feature(test)]
 
 extern crate alloc;
 
-extern crate libc as alloc;
+extern crate test as alloc;
 //~^ ERROR E0259
 
 fn main() {}
diff --git a/tests/ui/error-codes/E0259.stderr b/tests/ui/error-codes/E0259.stderr
index 6e086268fc6..975d1a161a0 100644
--- a/tests/ui/error-codes/E0259.stderr
+++ b/tests/ui/error-codes/E0259.stderr
@@ -4,13 +4,13 @@ error[E0259]: the name `alloc` is defined multiple times
 LL | extern crate alloc;
    | ------------------- previous import of the extern crate `alloc` here
 LL |
-LL | extern crate libc as alloc;
+LL | extern crate test as alloc;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ `alloc` reimported here
    |
    = note: `alloc` must be defined only once in the type namespace of this module
 help: you can use `as` to change the binding name of the import
    |
-LL | extern crate libc as other_alloc;
+LL | extern crate test as other_alloc;
    |
 
 error: aborting due to 1 previous error
diff --git a/tests/ui/imports/issue-37887.rs b/tests/ui/imports/issue-37887.rs
index 58f0c6b651a..919f46d34c6 100644
--- a/tests/ui/imports/issue-37887.rs
+++ b/tests/ui/imports/issue-37887.rs
@@ -1,4 +1,4 @@
 fn main() {
-    extern crate libc; //~ ERROR use of unstable
-    use libc::*; //~ ERROR unresolved import
+    extern crate test; //~ ERROR use of unstable
+    use test::*; //~ ERROR unresolved import
 }
diff --git a/tests/ui/imports/issue-37887.stderr b/tests/ui/imports/issue-37887.stderr
index 6117fd21af1..e7792ac0d15 100644
--- a/tests/ui/imports/issue-37887.stderr
+++ b/tests/ui/imports/issue-37887.stderr
@@ -1,19 +1,19 @@
-error[E0432]: unresolved import `libc`
+error[E0432]: unresolved import `test`
   --> $DIR/issue-37887.rs:3:9
    |
-LL |     use libc::*;
-   |         ^^^^ maybe a missing crate `libc`?
+LL |     use test::*;
+   |         ^^^^ maybe a missing crate `test`?
    |
-   = help: consider adding `extern crate libc` to use the `libc` crate
+   = help: consider adding `extern crate test` to use the `test` crate
 
-error[E0658]: use of unstable library feature 'rustc_private': this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
+error[E0658]: use of unstable library feature 'test'
   --> $DIR/issue-37887.rs:2:5
    |
-LL |     extern crate libc;
+LL |     extern crate test;
    |     ^^^^^^^^^^^^^^^^^^
    |
-   = note: see issue #27812 <https://github.com/rust-lang/rust/issues/27812> for more information
-   = help: add `#![feature(rustc_private)]` to the crate attributes to enable
+   = note: see issue #50297 <https://github.com/rust-lang/rust/issues/50297> for more information
+   = help: add `#![feature(test)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error: aborting due to 2 previous errors
diff --git a/tests/ui/lint/unnecessary-extern-crate.rs b/tests/ui/lint/unnecessary-extern-crate.rs
index 6ca3b96758f..7f97a4c469e 100644
--- a/tests/ui/lint/unnecessary-extern-crate.rs
+++ b/tests/ui/lint/unnecessary-extern-crate.rs
@@ -1,12 +1,12 @@
 //@ edition:2018
 
 #![deny(unused_extern_crates)]
-#![feature(test, rustc_private)]
+#![feature(test)]
 
-extern crate libc;
+extern crate core;
 //~^ ERROR unused extern crate
 //~| HELP remove
-extern crate libc as x;
+extern crate core as x;
 //~^ ERROR unused extern crate
 //~| HELP remove
 
@@ -28,11 +28,11 @@ mod foo {
 
     pub(super) extern crate alloc as d;
 
-    extern crate libc;
+    extern crate core;
     //~^ ERROR unused extern crate
     //~| HELP remove
 
-    extern crate libc as x;
+    extern crate core as x;
     //~^ ERROR unused extern crate
     //~| HELP remove
 
@@ -41,11 +41,11 @@ mod foo {
     pub extern crate test as y;
 
     mod bar {
-        extern crate libc;
+        extern crate core;
         //~^ ERROR unused extern crate
         //~| HELP remove
 
-        extern crate libc as x;
+        extern crate core as x;
         //~^ ERROR unused extern crate
         //~| HELP remove
 
diff --git a/tests/ui/lint/unnecessary-extern-crate.stderr b/tests/ui/lint/unnecessary-extern-crate.stderr
index 14ba9d052f4..1fa4aa9c9a9 100644
--- a/tests/ui/lint/unnecessary-extern-crate.stderr
+++ b/tests/ui/lint/unnecessary-extern-crate.stderr
@@ -1,7 +1,7 @@
 error: unused extern crate
   --> $DIR/unnecessary-extern-crate.rs:6:1
    |
-LL | extern crate libc;
+LL | extern crate core;
    | ^^^^^^^^^^^^^^^^^^ help: remove it
    |
 note: the lint level is defined here
@@ -13,31 +13,31 @@ LL | #![deny(unused_extern_crates)]
 error: unused extern crate
   --> $DIR/unnecessary-extern-crate.rs:9:1
    |
-LL | extern crate libc as x;
+LL | extern crate core as x;
    | ^^^^^^^^^^^^^^^^^^^^^^^ help: remove it
 
 error: unused extern crate
   --> $DIR/unnecessary-extern-crate.rs:31:5
    |
-LL |     extern crate libc;
+LL |     extern crate core;
    |     ^^^^^^^^^^^^^^^^^^ help: remove it
 
 error: unused extern crate
   --> $DIR/unnecessary-extern-crate.rs:35:5
    |
-LL |     extern crate libc as x;
+LL |     extern crate core as x;
    |     ^^^^^^^^^^^^^^^^^^^^^^^ help: remove it
 
 error: unused extern crate
   --> $DIR/unnecessary-extern-crate.rs:44:9
    |
-LL |         extern crate libc;
+LL |         extern crate core;
    |         ^^^^^^^^^^^^^^^^^^ help: remove it
 
 error: unused extern crate
   --> $DIR/unnecessary-extern-crate.rs:48:9
    |
-LL |         extern crate libc as x;
+LL |         extern crate core as x;
    |         ^^^^^^^^^^^^^^^^^^^^^^^ help: remove it
 
 error: aborting due to 6 previous errors
diff --git a/tests/ui/meta/no_std-extern-libc.rs b/tests/ui/meta/no_std-extern-libc.rs
index 919caf9428f..8b89e14382d 100644
--- a/tests/ui/meta/no_std-extern-libc.rs
+++ b/tests/ui/meta/no_std-extern-libc.rs
@@ -1,5 +1,6 @@
 // Test that `download-rustc` doesn't put duplicate copies of libc in the sysroot.
 //@ check-pass
+//@ ignore-windows doesn't necessarily have the libc crate
 #![crate_type = "lib"]
 #![no_std]
 #![feature(rustc_private)]
diff --git a/tests/ui/process/no-stdio.rs b/tests/ui/process/no-stdio.rs
index 05b1e52b799..8eebf6dbc7d 100644
--- a/tests/ui/process/no-stdio.rs
+++ b/tests/ui/process/no-stdio.rs
@@ -5,11 +5,13 @@
 
 #![feature(rustc_private)]
 
+#[cfg(unix)]
 extern crate libc;
 
-use std::process::{Command, Stdio};
 use std::env;
+use std::ffi::c_int;
 use std::io::{self, Read, Write};
+use std::process::{Command, Stdio};
 
 #[cfg(unix)]
 unsafe fn without_stdio<R, F: FnOnce() -> R>(f: F) -> R {
@@ -36,14 +38,14 @@ unsafe fn without_stdio<R, F: FnOnce() -> R>(f: F) -> R {
 }
 
 #[cfg(unix)]
-fn assert_fd_is_valid(fd: libc::c_int) {
+fn assert_fd_is_valid(fd: c_int) {
     if unsafe { libc::fcntl(fd, libc::F_GETFD) == -1 } {
         panic!("file descriptor {} is not valid: {}", fd, io::Error::last_os_error());
     }
 }
 
 #[cfg(windows)]
-fn assert_fd_is_valid(_fd: libc::c_int) {}
+fn assert_fd_is_valid(_fd: c_int) {}
 
 #[cfg(windows)]
 unsafe fn without_stdio<R, F: FnOnce() -> R>(f: F) -> R {
diff --git a/tests/ui/wait-forked-but-failed-child.rs b/tests/ui/wait-forked-but-failed-child.rs
index 3d052cc193c..dd6a7fa0e65 100644
--- a/tests/ui/wait-forked-but-failed-child.rs
+++ b/tests/ui/wait-forked-but-failed-child.rs
@@ -7,8 +7,6 @@
 
 #![feature(rustc_private)]
 
-extern crate libc;
-
 use std::process::Command;
 
 // The output from "ps -A -o pid,ppid,args" should look like this:
@@ -28,6 +26,7 @@
 
 #[cfg(unix)]
 fn find_zombies() {
+    extern crate libc;
     let my_pid = unsafe { libc::getpid() };
 
     // https://pubs.opengroup.org/onlinepubs/9699919799/utilities/ps.html