test: hide progress spinners in test runs

Steady-tick spinner threads redraw straight to the real stderr, bypassing
both the harness capture and the per-test log files: 'Scaffolding' lines
from the pkh new tests kept leaking between test results. The scaffold
tests now pass a hidden draw target (the only MultiProgress not created
by the CLI).

src/new/mod.rs

@@ -331,7 +331,12 @@ mod tests {
     ) -> Result<ScaffoldOutcome, Box<dyn Error>> {
         let previous = std::env::current_dir()?;
         std::env::set_current_dir(dir)?;
-        let result = scaffold(opts, &MultiProgress::new());
+        // Hidden draw target: in tests the spinner would redraw from its
+        // steady-tick thread straight to the real stderr
+        let result = scaffold(
+            opts,
+            &MultiProgress::with_draw_target(crate::ui::progress_draw_target()),
+        );
         std::env::set_current_dir(previous)?;
         result
     }

src/ui.rs

@@ -9,7 +9,11 @@ pub mod logfmt;
 /// yes/no confirmation
 pub mod prompt;
 
-use indicatif::{MultiProgress, ProgressBar, ProgressStyle};
+use indicatif::{
+    MultiProgress, ProgressBar, ProgressStyle,
+};
+#[cfg(test)]
+use indicatif::ProgressDrawTarget;
 use std::path::Path;
 use std::time::Duration;
 
@@ -38,6 +42,16 @@ pub(crate) fn spinner_style() -> ProgressStyle {
         .unwrap()
 }
 
+/// Progress draw target for a [`MultiProgress`]: hidden in test runs
+///
+/// Steady-tick spinners redraw from a background thread straight to the real
+/// stderr, bypassing both the test harness capture and the per-test log
+/// files; in tests there is no terminal to animate anyway.
+#[cfg(test)]
+pub(crate) fn progress_draw_target() -> ProgressDrawTarget {
+    ProgressDrawTarget::hidden()
+}
+
 /// Style of a sized transfer: prefix on the first line, the bar on its own
 /// indented line below so long prefixes cannot push it out of the terminal
 pub(crate) fn transfer_style() -> ProgressStyle {