assertions: use assert_eq! where possible

Using `assert_eq!` instead of `assert!` has the advantage that when the
assertion fails, the debug representation of both sides will be shown,
which can provide more information about the failure than only seeing
that the assertion failed.

Part of #12336

src/wutil/dir_iter.rs

@@ -269,7 +269,10 @@ pub fn next(&mut self) -> Option<io::Result<&DirEntry>> {
         };
 
         // dent.d_name is c_char; pretend it's u8.
-        assert!(std::mem::size_of::<libc::c_char>() == std::mem::size_of::<u8>());
+        assert_eq!(
+            std::mem::size_of::<libc::c_char>(),
+            std::mem::size_of::<u8>()
+        );
 
         // Do not rely on `libc::dirent::d_name.len()` as dirent names may exceed
         // the nominal buffer size; instead use the terminating nul byte.
@@ -463,8 +466,9 @@ fn test_dir_iter() {
             }
             // If we have a fast type, it should be correct.
             assert!(entry.fast_type().is_none() || entry.fast_type() == expected);
-            assert!(
-                entry.check_type() == expected,
+            assert_eq!(
+                entry.check_type(),
+                expected,
                 "Wrong type for {}. Expected {:?}, got {:?}",
                 entry.name,
                 expected,

src/wutil/mod.rs

@@ -685,7 +685,7 @@ fn test_wwrite_to_fd() {
                     input.len(),
                 )
             };
-            assert!(usize::try_from(read_amt).unwrap() == input.len());
+            assert_eq!(usize::try_from(read_amt).unwrap(), input.len());
             assert_eq!(&contents, &input);
         }
     }