From 8dd88c7b6b9fc27f2fb92c56903336d42c796cf0 Mon Sep 17 00:00:00 2001
From: zubin <79480850+zubincarvalho@users.noreply.github.com>
Date: Sun, 8 Nov 2026 23:51:35 -0800
Subject: [PATCH] Add tests for string offset arithmetic and StringRange

---
 crates/string-offset/src/lib_tests.rs | 75 ++++++++++++++++++++++++++-
 1 file changed, 74 insertions(+), 1 deletion(-)

diff --git a/crates/string-offset/src/lib_tests.rs b/crates/string-offset/src/lib_tests.rs
index 7c0c63e1c44..9ee6a668c3b 100644
--- a/crates/string-offset/src/lib_tests.rs
+++ b/crates/string-offset/src/lib_tests.rs
@@ -1,4 +1,6 @@
-use crate::CharCounter;
+use num_traits::SaturatingSub;
+
+use crate::{ByteOffset, CharCounter, CharOffset, StringRange};
 
 #[test]
 fn test_char_counter_sequential() {
@@ -49,3 +51,74 @@ fn test_char_counter_nonsequential() {
     // Skip ahead to the emoji.
     assert_eq!(counter.char_offset(9), Some(7.into()));
 }
+
+#[test]
+fn test_offset_arithmetic() {
+    let mut offset = CharOffset::from(5);
+    assert_eq!(offset + CharOffset::from(3), CharOffset::from(8));
+    assert_eq!(offset + 2, CharOffset::from(7));
+    assert_eq!(offset - CharOffset::from(2), CharOffset::from(3));
+    assert_eq!(offset - 5, CharOffset::zero());
+
+    offset += 4;
+    offset -= CharOffset::from(1);
+    assert_eq!(offset.as_usize(), 8);
+    assert_eq!(offset.to_string(), "8");
+}
+
+#[test]
+fn test_offset_add_signed() {
+    assert_eq!(ByteOffset::from(10).add_signed(-4), ByteOffset::from(6));
+    assert_eq!(ByteOffset::from(10).add_signed(4), ByteOffset::from(14));
+    assert_eq!(ByteOffset::from(3).add_signed(-3), ByteOffset::zero());
+}
+
+#[test]
+fn test_char_offset_add_assign_i32() {
+    let mut offset = CharOffset::from(5);
+    offset += 3;
+    assert_eq!(offset, CharOffset::from(8));
+    offset += -2i32;
+    assert_eq!(offset, CharOffset::from(6));
+}
+
+#[test]
+fn test_offset_saturating_sub() {
+    let small = ByteOffset::from(2);
+    let large = ByteOffset::from(7);
+    assert_eq!(large.saturating_sub(&small), ByteOffset::from(5));
+    assert_eq!(small.saturating_sub(&large), ByteOffset::zero());
+}
+
+#[test]
+fn test_offset_ranges() {
+    assert_eq!(
+        CharOffset::range(2..5),
+        CharOffset::from(2)..CharOffset::from(5)
+    );
+    let empty = ByteOffset::from(4).empty_range();
+    assert_eq!(empty, ByteOffset::from(4)..ByteOffset::from(4));
+    assert!(empty.is_empty());
+}
+
+#[test]
+fn test_extend_range_end() {
+    let mut range = StringRange {
+        char_range: 0..4,
+        byte_range: 0..6,
+    };
+    range.extend_range_end(&StringRange {
+        char_range: 2..7,
+        byte_range: 3..10,
+    });
+    assert_eq!(range.char_range, 0..7);
+    assert_eq!(range.byte_range, 0..10);
+
+    // A range that ends earlier must not shrink the current one.
+    range.extend_range_end(&StringRange {
+        char_range: 1..3,
+        byte_range: 1..4,
+    });
+    assert_eq!(range.char_range, 0..7);
+    assert_eq!(range.byte_range, 0..10);
+}