Function googletest::matchers::le

pub fn le<ActualT: Debug + PartialOrd<ExpectedT>, ExpectedT: Debug>(
    expected: ExpectedT
) -> impl Matcher<ActualT = ActualT>

Matches a value less than or equal to (in the sense of <=) expected.

The types of ActualT of actual and ExpectedT of expected must be comparable via the PartialOrd trait. Namely, ActualT must implement PartialOrd<ExpectedT>.

verify_that!(0, le(0))?; // Passes
verify_that!(1, le(0))?; // Fails

In most cases the params neeed to be the same type or they need to be cast explicitly. This can be surprising when comparing integer types or references:

verify_that!(1u32, le(2u64))?; // Does not compile
verify_that!(1u32 as u64, le(2u64))?; // Passes

let actual: &u32 = &1;
let expected: u32 = 2;
verify_that!(actual, le(expected))?; // Does not compile

let actual: &u32 = &1;
let expected: u32 = 2;
verify_that!(actual, le(&expected))?; // Compiles and passes

You can find the standard library PartialOrd implementation in https://doc.rust-lang.org/core/cmp/trait.PartialOrd.html#implementors