tests: add some no_run tests

Author: PatchMixolydic

src/lib.rs

@@ -8,3 +8,49 @@ mod linux;
 pub use linux::*;
 #[cfg(not(target_os = "linux"))]
 compile_error!("pidfds are currently only supported on Linux");
+
+#[cfg(any(test, doctest))]
+mod tests {
+    /// Used to allow for `no_run` tests.
+    ///
+    /// Using `pidfd`:
+    /// ```no_run (/usr/bin/foo likely does not exist and might close fd 1 regardless)
+    /// use pidfd::PidFd;
+    /// use pidfd_getfd::{GetFdFlags, PidFdExt};
+    /// use std::{io, process::Command};
+    ///
+    /// fn main() -> io::Result<()> {
+    ///     let child = Command::new("/usr/bin/foo").spawn().expect("failed to run `foo`");
+    ///     let pidfd = PidFd::from_std_checked(&child)?;
+    ///     let file_from_child = pidfd.get_file(1, GetFdFlags::empty())?;
+    ///     Ok(())
+    /// }
+    /// ```
+    struct _DocTests;
+
+    #[cfg(feature = "nightly")]
+    /// Used to allow for `no_run` tests.
+    ///
+    /// Using `std`'s `PidFd`:
+    /// ```no_run (/usr/bin/foo likely does not exist and might close fd 1 regardless)
+    /// #![feature(linux_pidfd)]
+    ///
+    /// use pidfd_getfd::{GetFdFlags, PidFdExt};
+    /// use std::{
+    ///     io,
+    ///     os::linux::process::{ChildExt, CommandExt},
+    ///     process::Command,
+    /// };
+    ///
+    /// fn main() -> io::Result<()> {
+    ///     let child = Command::new("/usr/bin/foo")
+    ///         .create_pidfd(true)
+    ///         .spawn()
+    ///         .expect("failed to run `foo`");
+    ///
+    ///     let file_from_child = child.pidfd()?.get_file(1, GetFdFlags::empty())?;
+    ///     Ok(())
+    /// }
+    /// ```
+    struct _NightlyDocTests;
+}