Fix incorrect highlighting when an empty range is highlighted via the DisplayMap

Co-Authored-By: Keith Simmons <keith@zed.dev>

crates/editor/src/test.rs

@@ -1,3 +1,5 @@
+use std::ops::Range;
+
 use collections::HashMap;
 
 #[cfg(test)]
@@ -31,3 +33,24 @@ pub fn marked_text(marked_text: &str) -> (String, Vec<usize>) {
     let (unmarked_text, mut markers) = marked_text_by(marked_text, vec!['|']);
     (unmarked_text, markers.remove(&'|').unwrap_or_else(Vec::new))
 }
+
+pub fn marked_text_ranges(
+    marked_text: &str,
+    range_markers: Vec<(char, char)>,
+) -> (String, Vec<Range<usize>>) {
+    let mut marker_chars = Vec::new();
+    for (start, end) in range_markers.iter() {
+        marker_chars.push(*start);
+        marker_chars.push(*end);
+    }
+    let (unmarked_text, markers) = marked_text_by(marked_text, marker_chars);
+    let ranges = range_markers
+        .iter()
+        .map(|(start_marker, end_marker)| {
+            let start = markers.get(start_marker).unwrap()[0];
+            let end = markers.get(end_marker).unwrap()[0];
+            start..end
+        })
+        .collect();
+    (unmarked_text, ranges)
+}