Allow the creation of build managers that cannot create nested builds

Author: oli-obk

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "ui_test"
-version = "0.26.4"
+version = "0.26.5"
 edition = "2021"
 license = "MIT OR Apache-2.0"
 description = "A test framework for testing rustc diagnostics output"

Cargo.toml

@@ -7,7 +7,7 @@ use std::{
 };
 
 use color_eyre::eyre::Result;
-use crossbeam_channel::Sender;
+use crossbeam_channel::{bounded, Sender};
 
 use crate::{
     status_emitter::{RevisionStyle, TestStatus},
@@ -47,6 +47,11 @@ impl BuildManager {
         }
     }
 
+    /// Create a new `BuildManager` that cannot create new sub-jobs.
+    pub fn one_off(config: Config) -> Self {
+        Self::new(config, bounded(0).0)
+    }
+
     /// Lazily add more jobs after a test has finished. These are added to the queue
     /// as normally, but nested below the test.
     pub fn add_new_job(&self, job: impl Send + 'static + FnOnce() -> TestRun) {