test(index): add unit tests to oxc_index (#5979)

Trying to improve `oxc_index`'s code coverage.

crates/oxc_index/src/lib.rs

@@ -795,3 +795,48 @@ impl<'de, I: Idx, T: serde::de::Deserialize<'de>> serde::de::Deserialize<'de> fo
         Box::<[T]>::deserialize(deserializer).map(Into::into)
     }
 }
+
+#[cfg(test)]
+#[allow(clippy::legacy_numeric_constants)]
+mod test {
+    use super::*;
+
+    define_index_type! {
+        pub struct TestIdx = u32;
+    }
+
+    #[test]
+    fn test_resize() {
+        let mut v = IndexVec::<TestIdx, u32>::with_capacity(10);
+        assert_eq!(v.len(), 0);
+        assert!(v.is_empty());
+
+        v.push(1);
+        assert_eq!(v.len(), 1);
+
+        v.resize(5, 1);
+        assert_eq!(v.len(), 5);
+        assert_eq!(v.as_slice(), &[1, 1, 1, 1, 1]);
+
+        v.shrink_to_fit();
+        assert_eq!(v.len(), 5);
+    }
+
+    #[test]
+    fn test_push_pop() {
+        let mut v = IndexVec::<TestIdx, u32>::new();
+        v.push(1);
+        assert_eq!(v.pop(), Some(1));
+    }
+
+    #[test]
+    fn test_clear() {
+        let mut v: IndexVec<TestIdx, u32> = [1, 2, 3].into_iter().collect();
+        assert_eq!(v.len(), 3);
+
+        v.clear();
+        assert_eq!(v.len(), 0);
+        assert_eq!(v.as_slice(), &[]);
+        assert_eq!(v, IndexVec::<TestIdx, u32>::new());
+    }
+}