The @assert macro actually exists in the standard library. The standard version also allows you to give your own error message, which is printed after ERROR: assertion failed.

The Test library contains some useful macros to compare the numbers:

using Test 
@test 1 == 3 

This returns the following:

Test Failed at REPL[5]:1
  Expression: 1 == 3
    Evaluated: 1 == 3
ERROR: There was an error during testing.

@test with the ≈ operator tests whether the two numbers are approximately equal. @test 1 ≈ 1.1 returns Test Failed because they are not equal within the machine tolerance. However, you can give the interval as the last argument within which they should be equal: @test 1 ≈ 1.1 atol=0.2, which returns Test Passed, so 1 and 1.1 are within 0.2 from each other.