Assert!(a == b) or assert_eq!(a, b)

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I’ve made some measurements comparing performance of assert! and assert_eq! on part of the Rust’s own test suite (namely, tests in src/test).

First, I replaced all the assert!s with assert_eq!s where possible on branch assert1, then replaced all assert_eq!s with assert!s on branch assert2 (the difference is approximately 2350 assertions), then I measured the time spent on compiling and running the tests. Here’s the results:

assert1:
real    7m27.344s
user    0m0.885s
sys     0m2.306s
assert2:
real    7m19.202s
user    0m1.299s
sys     0m4.011s
assert1:
real    7m22.374s
user    0m1.143s
sys     0m4.053s
assert2:
real    7m20.605s
user    0m1.285s
sys     0m4.339s
assert1:
real    7m23.646s
user    0m1.219s
sys     0m4.116s
assert2:
real    7m19.442s
user    0m1.390s
sys     0m3.978s

On average, the slowdown from assert_eq! is about 1%, which is quite acceptable given that assert_eq! is much more useful when something actually breaks.
I’ll open a pull request replacing assert! with assert_eq! in tests.

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