feat: push_str capacity exceeds error message

src/bounded_str.rs

@@ -159,16 +159,17 @@ impl<const N: usize, Alignment> BoundedStr<N, Alignment> {
   pub fn push_str(&mut self, s: &str) -> Result<(), ExceedsCapacity> {
     let bytes = s.as_bytes();
     let length = self.length as usize;
+    let new_len = length + bytes.len();
 
-    if length + bytes.len() > N {
+    if new_len > N {
       return Err(ExceedsCapacity {
-        length,
+        length: new_len,
         capacity: N,
       });
     }
 
-    self.data[length..length + bytes.len()].copy_from_slice(bytes);
-    self.length += bytes.len() as u8;
+    self.data[length..new_len].copy_from_slice(bytes);
+    self.length = new_len as u8;
 
     Ok(())
   }

src/tests/bounded_str_tests.rs

@@ -5,6 +5,7 @@ use crate::BStr15;
 use crate::BStr31;
 use crate::BStr63;
 use crate::BStr127;
+use crate::ExceedsCapacity;
 
 #[test]
 fn test_size() {
@@ -34,6 +35,19 @@ fn test_push_str() {
   assert_eq!(s.as_str(), "abcdef");
 }
 
+#[test]
+fn test_push_str_exceeds_capacity() {
+  let mut s = BStr7::new();
+
+  assert_eq!(
+    s.push_str("00000000"),
+    Err(ExceedsCapacity {
+      length: 8,
+      capacity: 7
+    })
+  );
+}
+
 #[test]
 fn test_push() {
   let mut s = BStr15::new();
@@ -61,11 +75,12 @@ fn test_into() {
 
 #[cfg(feature = "std")]
 mod std {
+  use std::format;
   use std::string::String;
   use std::vec;
   use std::vec::Vec;
 
-  use crate::{Align8, Align64, BStr7, BStr63, StrVec};
+  use crate::{Align8, Align64, BStr7, BStr63, ExceedsCapacity, StrVec};
 
   #[test]
   fn test_into_panic() {
@@ -114,6 +129,25 @@ mod std {
       ]
     );
   }
+
+  #[test]
+  fn test_push_str_exceeds_capacity() {
+    let mut s = BStr7::new();
+    let exceeds_capacity = s.push_str("00000000").unwrap_err();
+
+    assert_eq!(
+      exceeds_capacity,
+      ExceedsCapacity {
+        length: 8,
+        capacity: 7
+      }
+    );
+
+    assert_eq!(
+      format!("{}", exceeds_capacity),
+      "String length (8) exceeds capacity (7)"
+    );
+  }
 }
 
 #[cfg(feature = "serde")]