diff --git a/library/std/src/fs/tests.rs b/library/std/src/fs/tests.rs
index 28f16da1ed8d2..e3810030dedf7 100644
--- a/library/std/src/fs/tests.rs
+++ b/library/std/src/fs/tests.rs
@@ -14,7 +14,7 @@ use crate::os::unix::fs::symlink as junction_point;
 use crate::os::windows::fs::{OpenOptionsExt, junction_point, symlink_dir, symlink_file};
 use crate::path::Path;
 use crate::sync::Arc;
-use crate::sys_common::io::test::{TempDir, tmpdir};
+use crate::test_helpers::{TempDir, tmpdir};
 use crate::time::{Duration, Instant, SystemTime};
 use crate::{env, str, thread};
 
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index cfd03b8e3d6d0..0ffad2c27a4d5 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -344,7 +344,7 @@ pub mod prelude;
 mod stdio;
 mod util;
 
-const DEFAULT_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
+const DEFAULT_BUF_SIZE: usize = crate::sys::io::DEFAULT_BUF_SIZE;
 
 pub(crate) use stdio::cleanup;
 
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 7c18226874cc8..954a4182fbd6c 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -739,27 +739,4 @@ mod sealed {
 
 #[cfg(test)]
 #[allow(dead_code)] // Not used in all configurations.
-pub(crate) mod test_helpers {
-    /// Test-only replacement for `rand::thread_rng()`, which is unusable for
-    /// us, as we want to allow running stdlib tests on tier-3 targets which may
-    /// not have `getrandom` support.
-    ///
-    /// Does a bit of a song and dance to ensure that the seed is different on
-    /// each call (as some tests sadly rely on this), but doesn't try that hard.
-    ///
-    /// This is duplicated in the `core`, `alloc` test suites (as well as
-    /// `std`'s integration tests), but figuring out a mechanism to share these
-    /// seems far more painful than copy-pasting a 7 line function a couple
-    /// times, given that even under a perma-unstable feature, I don't think we
-    /// want to expose types from `rand` from `std`.
-    #[track_caller]
-    pub(crate) fn test_rng() -> rand_xorshift::XorShiftRng {
-        use core::hash::{BuildHasher, Hash, Hasher};
-        let mut hasher = crate::hash::RandomState::new().build_hasher();
-        core::panic::Location::caller().hash(&mut hasher);
-        let hc64 = hasher.finish();
-        let seed_vec = hc64.to_le_bytes().into_iter().chain(0u8..8).collect::<Vec<u8>>();
-        let seed: [u8; 16] = seed_vec.as_slice().try_into().unwrap();
-        rand::SeedableRng::from_seed(seed)
-    }
-}
+pub(crate) mod test_helpers;
diff --git a/library/std/src/os/unix/fs/tests.rs b/library/std/src/os/unix/fs/tests.rs
index 67f607bd46837..db9621c8c205c 100644
--- a/library/std/src/os/unix/fs/tests.rs
+++ b/library/std/src/os/unix/fs/tests.rs
@@ -3,7 +3,7 @@ use super::*;
 #[test]
 fn read_vectored_at() {
     let msg = b"preadv is working!";
-    let dir = crate::sys_common::io::test::tmpdir();
+    let dir = crate::test_helpers::tmpdir();
 
     let filename = dir.join("preadv.txt");
     {
@@ -31,7 +31,7 @@ fn read_vectored_at() {
 #[test]
 fn write_vectored_at() {
     let msg = b"pwritev is not working!";
-    let dir = crate::sys_common::io::test::tmpdir();
+    let dir = crate::test_helpers::tmpdir();
 
     let filename = dir.join("preadv.txt");
     {
diff --git a/library/std/src/os/unix/net/tests.rs b/library/std/src/os/unix/net/tests.rs
index 21e2176185d25..0398a535eb54a 100644
--- a/library/std/src/os/unix/net/tests.rs
+++ b/library/std/src/os/unix/net/tests.rs
@@ -7,7 +7,7 @@ use crate::os::android::net::{SocketAddrExt, UnixSocketExt};
 use crate::os::linux::net::{SocketAddrExt, UnixSocketExt};
 #[cfg(any(target_os = "android", target_os = "linux"))]
 use crate::os::unix::io::AsRawFd;
-use crate::sys_common::io::test::tmpdir;
+use crate::test_helpers::tmpdir;
 use crate::thread;
 use crate::time::Duration;
 
diff --git a/library/std/src/process/tests.rs b/library/std/src/process/tests.rs
index 1323aba38b7cc..1d7087301feec 100644
--- a/library/std/src/process/tests.rs
+++ b/library/std/src/process/tests.rs
@@ -697,7 +697,7 @@ fn debug_print() {
 #[test]
 #[cfg(windows)]
 fn run_bat_script() {
-    let tempdir = crate::sys_common::io::test::tmpdir();
+    let tempdir = crate::test_helpers::tmpdir();
     let script_path = tempdir.join("hello.cmd");
 
     crate::fs::write(&script_path, "@echo Hello, %~1!").unwrap();
@@ -716,7 +716,7 @@ fn run_bat_script() {
 #[test]
 #[cfg(windows)]
 fn run_canonical_bat_script() {
-    let tempdir = crate::sys_common::io::test::tmpdir();
+    let tempdir = crate::test_helpers::tmpdir();
     let script_path = tempdir.join("hello.cmd");
 
     crate::fs::write(&script_path, "@echo Hello, %~1!").unwrap();
diff --git a/library/std/src/sys/io/mod.rs b/library/std/src/sys/io/mod.rs
index 4605b56f8f16c..e00b479109f39 100644
--- a/library/std/src/sys/io/mod.rs
+++ b/library/std/src/sys/io/mod.rs
@@ -38,3 +38,7 @@ mod is_terminal {
 
 pub use io_slice::{IoSlice, IoSliceMut};
 pub use is_terminal::is_terminal;
+
+// Bare metal platforms usually have very small amounts of RAM
+// (in the order of hundreds of KB)
+pub const DEFAULT_BUF_SIZE: usize = if cfg!(target_os = "espidf") { 512 } else { 8 * 1024 };
diff --git a/library/std/src/sys/pal/sgx/stdio.rs b/library/std/src/sys/pal/sgx/stdio.rs
index 2e680e740fde3..e79a3d971c6be 100644
--- a/library/std/src/sys/pal/sgx/stdio.rs
+++ b/library/std/src/sys/pal/sgx/stdio.rs
@@ -62,7 +62,7 @@ impl io::Write for Stderr {
     }
 }
 
-pub const STDIN_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
+pub const STDIN_BUF_SIZE: usize = crate::sys::io::DEFAULT_BUF_SIZE;
 
 pub fn is_ebadf(err: &io::Error) -> bool {
     // FIXME: Rust normally maps Unix EBADF to `Uncategorized`
diff --git a/library/std/src/sys/pal/unix/kernel_copy/tests.rs b/library/std/src/sys/pal/unix/kernel_copy/tests.rs
index 1350d743ff6f3..54d8f8ed2edd4 100644
--- a/library/std/src/sys/pal/unix/kernel_copy/tests.rs
+++ b/library/std/src/sys/pal/unix/kernel_copy/tests.rs
@@ -2,7 +2,7 @@ use crate::fs::OpenOptions;
 use crate::io;
 use crate::io::{BufRead, Read, Result, Seek, SeekFrom, Write};
 use crate::os::unix::io::AsRawFd;
-use crate::sys_common::io::test::tmpdir;
+use crate::test_helpers::tmpdir;
 
 #[test]
 fn copy_specialization() -> Result<()> {
diff --git a/library/std/src/sys/pal/unix/stdio.rs b/library/std/src/sys/pal/unix/stdio.rs
index 97e75f1b5b669..8c2f61a40de3b 100644
--- a/library/std/src/sys/pal/unix/stdio.rs
+++ b/library/std/src/sys/pal/unix/stdio.rs
@@ -92,7 +92,7 @@ pub fn is_ebadf(err: &io::Error) -> bool {
     err.raw_os_error() == Some(libc::EBADF as i32)
 }
 
-pub const STDIN_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
+pub const STDIN_BUF_SIZE: usize = crate::sys::io::DEFAULT_BUF_SIZE;
 
 pub fn panic_output() -> Option<impl io::Write> {
     Some(Stderr::new())
diff --git a/library/std/src/sys/pal/wasi/stdio.rs b/library/std/src/sys/pal/wasi/stdio.rs
index ca49f871e1957..d08b772e5fc7d 100644
--- a/library/std/src/sys/pal/wasi/stdio.rs
+++ b/library/std/src/sys/pal/wasi/stdio.rs
@@ -101,7 +101,7 @@ impl io::Write for Stderr {
     }
 }
 
-pub const STDIN_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
+pub const STDIN_BUF_SIZE: usize = crate::sys::io::DEFAULT_BUF_SIZE;
 
 pub fn is_ebadf(err: &io::Error) -> bool {
     err.raw_os_error() == Some(wasi::ERRNO_BADF.raw().into())
diff --git a/library/std/src/sys/pal/windows/process/tests.rs b/library/std/src/sys/pal/windows/process/tests.rs
index 1bcc5fa6b2048..9a1eaf42fd9a8 100644
--- a/library/std/src/sys/pal/windows/process/tests.rs
+++ b/library/std/src/sys/pal/windows/process/tests.rs
@@ -158,7 +158,7 @@ fn windows_exe_resolver() {
     use super::resolve_exe;
     use crate::io;
     use crate::sys::fs::symlink;
-    use crate::sys_common::io::test::tmpdir;
+    use crate::test_helpers::tmpdir;
 
     let env_paths = || env::var_os("PATH");
 
diff --git a/library/std/src/sys/pal/zkvm/stdio.rs b/library/std/src/sys/pal/zkvm/stdio.rs
index dd218c8894ca5..5f1d06dd1d78d 100644
--- a/library/std/src/sys/pal/zkvm/stdio.rs
+++ b/library/std/src/sys/pal/zkvm/stdio.rs
@@ -54,7 +54,7 @@ impl io::Write for Stderr {
     }
 }
 
-pub const STDIN_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
+pub const STDIN_BUF_SIZE: usize = crate::sys::io::DEFAULT_BUF_SIZE;
 
 pub fn is_ebadf(_err: &io::Error) -> bool {
     true
diff --git a/library/std/src/sys_common/io.rs b/library/std/src/sys_common/io.rs
deleted file mode 100644
index 6f6f282d432d6..0000000000000
--- a/library/std/src/sys_common/io.rs
+++ /dev/null
@@ -1,49 +0,0 @@
-// Bare metal platforms usually have very small amounts of RAM
-// (in the order of hundreds of KB)
-pub const DEFAULT_BUF_SIZE: usize = if cfg!(target_os = "espidf") { 512 } else { 8 * 1024 };
-
-#[cfg(test)]
-#[allow(dead_code)] // not used on emscripten and wasi
-pub mod test {
-    use rand::RngCore;
-
-    use crate::path::{Path, PathBuf};
-    use crate::{env, fs, thread};
-
-    pub struct TempDir(PathBuf);
-
-    impl TempDir {
-        pub fn join(&self, path: &str) -> PathBuf {
-            let TempDir(ref p) = *self;
-            p.join(path)
-        }
-
-        pub fn path(&self) -> &Path {
-            let TempDir(ref p) = *self;
-            p
-        }
-    }
-
-    impl Drop for TempDir {
-        fn drop(&mut self) {
-            // Gee, seeing how we're testing the fs module I sure hope that we
-            // at least implement this correctly!
-            let TempDir(ref p) = *self;
-            let result = fs::remove_dir_all(p);
-            // Avoid panicking while panicking as this causes the process to
-            // immediately abort, without displaying test results.
-            if !thread::panicking() {
-                result.unwrap();
-            }
-        }
-    }
-
-    #[track_caller] // for `test_rng`
-    pub fn tmpdir() -> TempDir {
-        let p = env::temp_dir();
-        let mut r = crate::test_helpers::test_rng();
-        let ret = p.join(&format!("rust-{}", r.next_u32()));
-        fs::create_dir(&ret).unwrap();
-        TempDir(ret)
-    }
-}
diff --git a/library/std/src/sys_common/mod.rs b/library/std/src/sys_common/mod.rs
index 959fbd4ca0a11..4dc67d26bd8ff 100644
--- a/library/std/src/sys_common/mod.rs
+++ b/library/std/src/sys_common/mod.rs
@@ -21,7 +21,6 @@
 mod tests;
 
 pub mod fs;
-pub mod io;
 pub mod process;
 pub mod wstr;
 pub mod wtf8;
diff --git a/library/std/src/test_helpers.rs b/library/std/src/test_helpers.rs
new file mode 100644
index 0000000000000..7c20f38c863b6
--- /dev/null
+++ b/library/std/src/test_helpers.rs
@@ -0,0 +1,65 @@
+use rand::{RngCore, SeedableRng};
+
+use crate::hash::{BuildHasher, Hash, Hasher, RandomState};
+use crate::panic::Location;
+use crate::path::{Path, PathBuf};
+use crate::{env, fs, thread};
+
+/// Test-only replacement for `rand::thread_rng()`, which is unusable for
+/// us, as we want to allow running stdlib tests on tier-3 targets which may
+/// not have `getrandom` support.
+///
+/// Does a bit of a song and dance to ensure that the seed is different on
+/// each call (as some tests sadly rely on this), but doesn't try that hard.
+///
+/// This is duplicated in the `core`, `alloc` test suites (as well as
+/// `std`'s integration tests), but figuring out a mechanism to share these
+/// seems far more painful than copy-pasting a 7 line function a couple
+/// times, given that even under a perma-unstable feature, I don't think we
+/// want to expose types from `rand` from `std`.
+#[track_caller]
+pub(crate) fn test_rng() -> rand_xorshift::XorShiftRng {
+    let mut hasher = RandomState::new().build_hasher();
+    Location::caller().hash(&mut hasher);
+    let hc64 = hasher.finish();
+    let seed_vec = hc64.to_le_bytes().into_iter().chain(0u8..8).collect::<Vec<u8>>();
+    let seed: [u8; 16] = seed_vec.as_slice().try_into().unwrap();
+    SeedableRng::from_seed(seed)
+}
+
+pub struct TempDir(PathBuf);
+
+impl TempDir {
+    pub fn join(&self, path: &str) -> PathBuf {
+        let TempDir(ref p) = *self;
+        p.join(path)
+    }
+
+    pub fn path(&self) -> &Path {
+        let TempDir(ref p) = *self;
+        p
+    }
+}
+
+impl Drop for TempDir {
+    fn drop(&mut self) {
+        // Gee, seeing how we're testing the fs module I sure hope that we
+        // at least implement this correctly!
+        let TempDir(ref p) = *self;
+        let result = fs::remove_dir_all(p);
+        // Avoid panicking while panicking as this causes the process to
+        // immediately abort, without displaying test results.
+        if !thread::panicking() {
+            result.unwrap();
+        }
+    }
+}
+
+#[track_caller] // for `test_rng`
+pub fn tmpdir() -> TempDir {
+    let p = env::temp_dir();
+    let mut r = test_rng();
+    let ret = p.join(&format!("rust-{}", r.next_u32()));
+    fs::create_dir(&ret).unwrap();
+    TempDir(ret)
+}
diff --git a/library/std/tests/common/mod.rs b/library/std/tests/common/mod.rs
index 7cf70c725e411..1e8e4cced6c03 100644
--- a/library/std/tests/common/mod.rs
+++ b/library/std/tests/common/mod.rs
@@ -18,7 +18,7 @@ pub(crate) fn test_rng() -> rand_xorshift::XorShiftRng {
     rand::SeedableRng::from_seed(seed)
 }
 
-// Copied from std::sys_common::io
+// Copied from std::test_helpers
 pub(crate) struct TempDir(PathBuf);
 
 impl TempDir {