write the remaining test fake executables from a child process

swarmctl/src/main.rs

@@ -1573,6 +1573,24 @@ mod tests {
         fs::remove_dir_all(&dir).ok();
     }
 
+    /// Write the script `body` to `path` as an executable, from a child process
+    /// rather than from this one: a write fd on it held here could be inherited
+    /// by a child another test thread forks, and exec'ing a file some process
+    /// still holds open for writing fails with `ETXTBSY`.
+    fn write_executable(path: &std::path::Path, body: &str) {
+        let status = std::process::Command::new("/bin/sh")
+            .args([
+                "-c",
+                r#"printf '%s' "$1" > "$2" && chmod 755 "$2""#,
+                "sh",
+                body,
+            ])
+            .arg(path)
+            .status()
+            .expect("run /bin/sh");
+        assert!(status.success(), "writing {} failed", path.display());
+    }
+
     /// A scratch directory holding a `users.yml` with one user, `carol`, and
     /// a stand-in `authelia` that takes `delay` seconds to mint a password.
     fn locked_users_fixture(tag: &str, delay: &str) -> Paths {
@@ -1580,14 +1598,12 @@ mod tests {
         let _ = fs::remove_dir_all(&dir);
         fs::create_dir_all(&dir).expect("temp dir");
         let authelia_bin = dir.join("authelia");
-        fs::write(
+        write_executable(
             &authelia_bin,
-            format!(
+            &format!(
                 "#!/bin/sh\nsleep {delay}\nprintf 'Random Password: pw\\nDigest: $argon2id$x\\n'\n"
             ),
-        )
-        .expect("fake authelia");
-        fs::set_permissions(&authelia_bin, Permissions::from_mode(0o755)).expect("chmod");
+        );
         let users_file = dir.join("users.yml");
         fs::write(
             &users_file,