Add integer to string formatting tests

Author: GuillaumeGomez

library/alloc/src/string.rs

@@ -3425,3 +3425,63 @@ impl From<char> for String {
         c.to_string()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use std::str::FromStr;
+
+    fn assert_nb<Int: ToString + FromStr>(value: Int) {
+        let s = value.to_string();
+        let s2 = format!("{}", value);
+
+        assert_eq!(s, s2);
+        let ret = Int::from_str(&s).unwrap();
+        assert_eq!(ret, int);
+    }
+
+    macro_rules! uint_to_s {
+        ($($fn_name:ident, $int:ident,)+) => {
+            $(
+                #[test]
+                fn $fn_name() {
+                    assert_nb::<$int>($int::MIN);
+                    assert_nb::<$int>($int::MAX);
+                    assert_nb::<$int>(1);
+                    assert_nb::<$int>($int::MIN / 2);
+                    assert_nb::<$int>($int::MAX / 2);
+                }
+            )+
+        }
+    }
+    macro_rules! int_to_s {
+        ($($fn_name:ident, $int:ident,)+) => {
+            $(
+                #[test]
+                fn $fn_name() {
+                    assert_nb::<$int>($int::MIN);
+                    assert_nb::<$int>($int::MAX);
+                    assert_nb::<$int>(1);
+                    assert_nb::<$int>(0);
+                    assert_nb::<$int>(-1);
+                    assert_nb::<$int>($int::MIN / 2);
+                    assert_nb::<$int>($int::MAX / 2);
+                }
+            )+
+        }
+    }
+
+    int_to_s!(
+        test_i8_to_string, i8,
+        test_i16_to_string, i16,
+        test_i32_to_string, i32,
+        test_i64_to_string, i64,
+        test_i128_to_string, i128,
+    );
+    uint_to_s!(
+        test_u8_to_string, u8,
+        test_u16_to_string, u16,
+        test_u32_to_string, u32,
+        test_u64_to_string, u64,
+        test_u128_to_string, u128,
+    );
+}