Fix a test flake involving zeroed out group_intervals (#20328)

Release Notes:

- N/A

crates/editor/src/editor_tests.rs

@@ -169,8 +169,12 @@ fn test_undo_redo_with_selection_restoration(cx: &mut TestAppContext) {
     init_test(cx, |_| {});
 
     let mut now = Instant::now();
-    let buffer = cx.new_model(|cx| language::Buffer::local("123456", cx));
-    let group_interval = buffer.update(cx, |buffer, _| buffer.transaction_group_interval());
+    let group_interval = Duration::from_millis(1);
+    let buffer = cx.new_model(|cx| {
+        let mut buf = language::Buffer::local("123456", cx);
+        buf.set_group_interval(group_interval);
+        buf
+    });
     let buffer = cx.new_model(|cx| MultiBuffer::singleton(buffer, cx));
     let editor = cx.add_window(|cx| build_editor(buffer.clone(), cx));
 

crates/multi_buffer/src/multi_buffer.rs

@@ -6482,11 +6482,21 @@ mod tests {
     fn test_history(cx: &mut AppContext) {
         let test_settings = SettingsStore::test(cx);
         cx.set_global(test_settings);
-
-        let buffer_1 = cx.new_model(|cx| Buffer::local("1234", cx));
-        let buffer_2 = cx.new_model(|cx| Buffer::local("5678", cx));
+        let group_interval: Duration = Duration::from_millis(1);
+        let buffer_1 = cx.new_model(|cx| {
+            let mut buf = Buffer::local("1234", cx);
+            buf.set_group_interval(group_interval);
+            buf
+        });
+        let buffer_2 = cx.new_model(|cx| {
+            let mut buf = Buffer::local("5678", cx);
+            buf.set_group_interval(group_interval);
+            buf
+        });
         let multibuffer = cx.new_model(|_| MultiBuffer::new(Capability::ReadWrite));
-        let group_interval = multibuffer.read(cx).history.group_interval;
+        multibuffer.update(cx, |this, _| {
+            this.history.group_interval = group_interval;
+        });
         multibuffer.update(cx, |multibuffer, cx| {
             multibuffer.push_excerpts(
                 buffer_1.clone(),

crates/text/src/tests.rs

@@ -608,6 +608,7 @@ fn test_history() {
 fn test_finalize_last_transaction() {
     let now = Instant::now();
     let mut buffer = Buffer::new(0, BufferId::new(1).unwrap(), "123456".into());
+    buffer.history.group_interval = Duration::from_millis(1);
 
     buffer.start_transaction_at(now);
     buffer.edit([(2..4, "cd")]);

crates/text/src/text.rs

@@ -227,7 +227,7 @@ impl History {
         if let Some(mut entry) = entries.next_back() {
             while let Some(prev_entry) = entries.next_back() {
                 if !prev_entry.suppress_grouping
-                    && entry.first_edit_at - prev_entry.last_edit_at <= self.group_interval
+                    && entry.first_edit_at - prev_entry.last_edit_at < self.group_interval
                 {
                     entry = prev_entry;
                     count += 1;