Use assert_matches! instead of if let {} else

4 files changed, 269 insertions, 292 deletions

diff --git a/library/alloc/tests/lib.rs b/library/alloc/tests/lib.rs
index b3e048a6587..8fca2662fc3 100644
--- a/library/alloc/tests/lib.rs
+++ b/library/alloc/tests/lib.rs
@@ -1,4 +1,5 @@
 #![feature(allocator_api)]
+#![feature(assert_matches)]
 #![feature(box_syntax)]
 #![feature(cow_is_borrowed)]
 #![feature(const_cow_is_borrowed)]
diff --git a/library/alloc/tests/string.rs b/library/alloc/tests/string.rs
index cf9d734a9d5..7be137131ff 100644
--- a/library/alloc/tests/string.rs
+++ b/library/alloc/tests/string.rs
@@ -1,3 +1,4 @@
+use std::assert_matches::assert_matches;
 use std::borrow::Cow;
 use std::cell::Cell;
 use std::collections::TryReserveErrorKind::*;
@@ -713,35 +714,32 @@ fn test_try_reserve() {
 
         if guards_against_isize {
             // Check isize::MAX + 1 does count as overflow
-            if let Err(CapacityOverflow) =
-                empty_string.try_reserve(MAX_CAP + 1).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!")
-            }
+            assert_matches!(
+                empty_string.try_reserve(MAX_CAP + 1).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
 
             // Check usize::MAX does count as overflow
-            if let Err(CapacityOverflow) = empty_string.try_reserve(MAX_USIZE).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("usize::MAX should trigger an overflow!")
-            }
+            assert_matches!(
+                empty_string.try_reserve(MAX_USIZE).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "usize::MAX should trigger an overflow!"
+            );
         } else {
             // Check isize::MAX + 1 is an OOM
-            if let Err(AllocError { .. }) =
-                empty_string.try_reserve(MAX_CAP + 1).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
+            assert_matches!(
+                empty_string.try_reserve(MAX_CAP + 1).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
 
             // Check usize::MAX is an OOM
-            if let Err(AllocError { .. }) =
-                empty_string.try_reserve(MAX_USIZE).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("usize::MAX should trigger an OOM!")
-            }
+            assert_matches!(
+                empty_string.try_reserve(MAX_USIZE).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "usize::MAX should trigger an OOM!"
+            );
         }
     }
 
@@ -756,23 +754,24 @@ fn test_try_reserve() {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!");
-            }
+            assert_matches!(
+                ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
         } else {
-            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
+            assert_matches!(
+                ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
         }
         // Should always overflow in the add-to-len
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind()) {
-        } else {
-            panic!("usize::MAX should trigger an overflow!")
-        }
+        assert_matches!(
+            ten_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind()),
+            Err(CapacityOverflow),
+            "usize::MAX should trigger an overflow!"
+        );
     }
 }
 
@@ -801,33 +800,29 @@ fn test_try_reserve_exact() {
         }
 
         if guards_against_isize {
-            if let Err(CapacityOverflow) =
-                empty_string.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!")
-            }
-
-            if let Err(CapacityOverflow) =
-                empty_string.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("usize::MAX should trigger an overflow!")
-            }
+            assert_matches!(
+                empty_string.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
+
+            assert_matches!(
+                empty_string.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "usize::MAX should trigger an overflow!"
+            );
         } else {
-            if let Err(AllocError { .. }) =
-                empty_string.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
-
-            if let Err(AllocError { .. }) =
-                empty_string.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("usize::MAX should trigger an OOM!")
-            }
+            assert_matches!(
+                empty_string.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
+
+            assert_matches!(
+                empty_string.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "usize::MAX should trigger an OOM!"
+            );
         }
     }
 
@@ -845,25 +840,23 @@ fn test_try_reserve_exact() {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) =
-                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!");
-            }
-        } else {
-            if let Err(AllocError { .. }) =
-                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
-        }
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
-        {
+            assert_matches!(
+                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
         } else {
-            panic!("usize::MAX should trigger an overflow!")
+            assert_matches!(
+                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
         }
+        assert_matches!(
+            ten_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind()),
+            Err(CapacityOverflow),
+            "usize::MAX should trigger an overflow!"
+        );
     }
 }
 
diff --git a/library/alloc/tests/vec.rs b/library/alloc/tests/vec.rs
index d3a6dcfddc5..c2df50b48f5 100644
--- a/library/alloc/tests/vec.rs
+++ b/library/alloc/tests/vec.rs
@@ -1,3 +1,4 @@
+use std::assert_matches::assert_matches;
 use std::borrow::Cow;
 use std::cell::Cell;
 use std::collections::TryReserveErrorKind::*;
@@ -1488,34 +1489,32 @@ fn test_try_reserve() {
 
         if guards_against_isize {
             // Check isize::MAX + 1 does count as overflow
-            if let Err(CapacityOverflow) =
-                empty_bytes.try_reserve(MAX_CAP + 1).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!")
-            }
+            assert_matches!(
+                empty_bytes.try_reserve(MAX_CAP + 1).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
 
             // Check usize::MAX does count as overflow
-            if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("usize::MAX should trigger an overflow!")
-            }
+            assert_matches!(
+                empty_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "usize::MAX should trigger an overflow!"
+            );
         } else {
             // Check isize::MAX + 1 is an OOM
-            if let Err(AllocError { .. }) =
-                empty_bytes.try_reserve(MAX_CAP + 1).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
+            assert_matches!(
+                empty_bytes.try_reserve(MAX_CAP + 1).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
 
             // Check usize::MAX is an OOM
-            if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("usize::MAX should trigger an OOM!")
-            }
+            assert_matches!(
+                empty_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "usize::MAX should trigger an OOM!"
+            );
         }
     }
 
@@ -1530,23 +1529,24 @@ fn test_try_reserve() {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!");
-            }
+            assert_matches!(
+                ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
         } else {
-            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
+            assert_matches!(
+                ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
         }
         // Should always overflow in the add-to-len
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind()) {
-        } else {
-            panic!("usize::MAX should trigger an overflow!")
-        }
+        assert_matches!(
+            ten_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind()),
+            Err(CapacityOverflow),
+            "usize::MAX should trigger an overflow!"
+        );
     }
 
     {
@@ -1562,25 +1562,24 @@ fn test_try_reserve() {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) =
-                ten_u32s.try_reserve(MAX_CAP / 4 - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!");
-            }
+            assert_matches!(
+                ten_u32s.try_reserve(MAX_CAP / 4 - 9).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
         } else {
-            if let Err(AllocError { .. }) =
-                ten_u32s.try_reserve(MAX_CAP / 4 - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
+            assert_matches!(
+                ten_u32s.try_reserve(MAX_CAP / 4 - 9).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
         }
         // Should fail in the mul-by-size
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_USIZE - 20).map_err(|e| e.kind()) {
-        } else {
-            panic!("usize::MAX should trigger an overflow!");
-        }
+        assert_matches!(
+            ten_u32s.try_reserve(MAX_USIZE - 20).map_err(|e| e.kind()),
+            Err(CapacityOverflow),
+            "usize::MAX should trigger an overflow!"
+        );
     }
 }
 
@@ -1609,33 +1608,29 @@ fn test_try_reserve_exact() {
         }
 
         if guards_against_isize {
-            if let Err(CapacityOverflow) =
-                empty_bytes.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!")
-            }
-
-            if let Err(CapacityOverflow) =
-                empty_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("usize::MAX should trigger an overflow!")
-            }
+            assert_matches!(
+                empty_bytes.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
+
+            assert_matches!(
+                empty_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "usize::MAX should trigger an overflow!"
+            );
         } else {
-            if let Err(AllocError { .. }) =
-                empty_bytes.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
+            assert_matches!(
+                empty_bytes.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
 
-            if let Err(AllocError { .. }) =
-                empty_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("usize::MAX should trigger an OOM!")
-            }
+            assert_matches!(
+                empty_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "usize::MAX should trigger an OOM!"
+            );
         }
     }
 
@@ -1653,25 +1648,23 @@ fn test_try_reserve_exact() {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) =
-                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!");
-            }
-        } else {
-            if let Err(AllocError { .. }) =
-                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
-        }
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
-        {
+            assert_matches!(
+                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
         } else {
-            panic!("usize::MAX should trigger an overflow!")
+            assert_matches!(
+                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
         }
+        assert_matches!(
+            ten_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind()),
+            Err(CapacityOverflow),
+            "usize::MAX should trigger an overflow!"
+        );
     }
 
     {
@@ -1688,26 +1681,23 @@ fn test_try_reserve_exact() {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) =
-                ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!");
-            }
+            assert_matches!(
+                ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
         } else {
-            if let Err(AllocError { .. }) =
-                ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
-        }
-        if let Err(CapacityOverflow) =
-            ten_u32s.try_reserve_exact(MAX_USIZE - 20).map_err(|e| e.kind())
-        {
-        } else {
-            panic!("usize::MAX should trigger an overflow!")
-        }
+            assert_matches!(
+                ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
+        }
+        assert_matches!(
+            ten_u32s.try_reserve_exact(MAX_USIZE - 20).map_err(|e| e.kind()),
+            Err(CapacityOverflow),
+            "usize::MAX should trigger an overflow!"
+        );
     }
 }
 
diff --git a/library/alloc/tests/vec_deque.rs b/library/alloc/tests/vec_deque.rs
index e9fd19d76ea..ddfb4c00c26 100644
--- a/library/alloc/tests/vec_deque.rs
+++ b/library/alloc/tests/vec_deque.rs
@@ -1,3 +1,4 @@
+use std::assert_matches::assert_matches;
 use std::collections::TryReserveErrorKind::*;
 use std::collections::{vec_deque::Drain, VecDeque};
 use std::fmt::Debug;
@@ -1181,28 +1182,28 @@ fn test_try_reserve() {
 
         if guards_against_isize {
             // Check isize::MAX + 1 does count as overflow
-            if let Err(CapacityOverflow) =
-                empty_bytes.try_reserve(MAX_CAP + 1).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!")
-            }
+            assert_matches!(
+                empty_bytes.try_reserve(MAX_CAP + 1).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
 
             // Check usize::MAX does count as overflow
-            if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("usize::MAX should trigger an overflow!")
-            }
+            assert_matches!(
+                empty_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "usize::MAX should trigger an overflow!"
+            );
         } else {
             // Check isize::MAX is an OOM
             // VecDeque starts with capacity 7, always adds 1 to the capacity
             // and also rounds the number to next power of 2 so this is the
             // furthest we can go without triggering CapacityOverflow
-            if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_CAP).map_err(|e| e.kind()) {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
+            assert_matches!(
+                empty_bytes.try_reserve(MAX_CAP).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
         }
     }
 
@@ -1217,23 +1218,24 @@ fn test_try_reserve() {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!");
-            }
+            assert_matches!(
+                ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
         } else {
-            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
+            assert_matches!(
+                ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
         }
         // Should always overflow in the add-to-len
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind()) {
-        } else {
-            panic!("usize::MAX should trigger an overflow!")
-        }
+        assert_matches!(
+            ten_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind()),
+            Err(CapacityOverflow),
+            "usize::MAX should trigger an overflow!"
+        );
     }
 
     {
@@ -1249,25 +1251,24 @@ fn test_try_reserve() {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) =
-                ten_u32s.try_reserve(MAX_CAP / 4 - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!");
-            }
+            assert_matches!(
+                ten_u32s.try_reserve(MAX_CAP / 4 - 9).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
         } else {
-            if let Err(AllocError { .. }) =
-                ten_u32s.try_reserve(MAX_CAP / 4 - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
+            assert_matches!(
+                ten_u32s.try_reserve(MAX_CAP / 4 - 9).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
         }
         // Should fail in the mul-by-size
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_USIZE - 20).map_err(|e| e.kind()) {
-        } else {
-            panic!("usize::MAX should trigger an overflow!");
-        }
+        assert_matches!(
+            ten_u32s.try_reserve(MAX_USIZE - 20).map_err(|e| e.kind()),
+            Err(CapacityOverflow),
+            "usize::MAX should trigger an overflow!"
+        );
     }
 }
 
@@ -1296,30 +1297,27 @@ fn test_try_reserve_exact() {
         }
 
         if guards_against_isize {
-            if let Err(CapacityOverflow) =
-                empty_bytes.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!")
-            }
-
-            if let Err(CapacityOverflow) =
-                empty_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("usize::MAX should trigger an overflow!")
-            }
+            assert_matches!(
+                empty_bytes.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
+
+            assert_matches!(
+                empty_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "usize::MAX should trigger an overflow!"
+            );
         } else {
             // Check isize::MAX is an OOM
             // VecDeque starts with capacity 7, always adds 1 to the capacity
             // and also rounds the number to next power of 2 so this is the
             // furthest we can go without triggering CapacityOverflow
-            if let Err(AllocError { .. }) =
-                empty_bytes.try_reserve_exact(MAX_CAP).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
+            assert_matches!(
+                empty_bytes.try_reserve_exact(MAX_CAP).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
         }
     }
 
@@ -1337,25 +1335,23 @@ fn test_try_reserve_exact() {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) =
-                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!");
-            }
-        } else {
-            if let Err(AllocError { .. }) =
-                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
-        }
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
-        {
+            assert_matches!(
+                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
         } else {
-            panic!("usize::MAX should trigger an overflow!")
+            assert_matches!(
+                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
         }
+        assert_matches!(
+            ten_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind()),
+            Err(CapacityOverflow),
+            "usize::MAX should trigger an overflow!"
+        );
     }
 
     {
@@ -1372,26 +1368,23 @@ fn test_try_reserve_exact() {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) =
-                ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an overflow!");
-            }
-        } else {
-            if let Err(AllocError { .. }) =
-                ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9).map_err(|e| e.kind())
-            {
-            } else {
-                panic!("isize::MAX + 1 should trigger an OOM!")
-            }
-        }
-        if let Err(CapacityOverflow) =
-            ten_u32s.try_reserve_exact(MAX_USIZE - 20).map_err(|e| e.kind())
-        {
+            assert_matches!(
+                ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9).map_err(|e| e.kind()),
+                Err(CapacityOverflow),
+                "isize::MAX + 1 should trigger an overflow!"
+            );
         } else {
-            panic!("usize::MAX should trigger an overflow!")
+            assert_matches!(
+                ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9).map_err(|e| e.kind()),
+                Err(AllocError { .. }),
+                "isize::MAX + 1 should trigger an OOM!"
+            );
         }
+        assert_matches!(
+            ten_u32s.try_reserve_exact(MAX_USIZE - 20).map_err(|e| e.kind()),
+            Err(CapacityOverflow),
+            "usize::MAX should trigger an overflow!"
+        );
     }
 }