Catch v2.0.1 - CHECK(-0.0019569472 == Approx(0.0).epsilon(0.1)); does not work

[mariusz102102]

Description

Regression v2.0.1 compare v1.9.7

Steps to reproduce

TEST_CASE("Test weight")
{
    CHECK(-0.0019569472 == Approx(0.0).epsilon(0.1));
}

g:\test\test.cpp(91): FAILED:
  CHECK( -0.0019569472 == Approx(0.0).epsilon(0.1) )
with expansion:
  -0.0019569472 == Approx( 0.0 )

Extra information

Below test case fails on v2.0.1 passed in catch v1.9.7

• Catch version: v2.0.1
• Operating System: *Windows 10 **
• Compiler+version: Visual studio 15.4

[horenmar]

This is actually an intended change, called out in the "breaking changes" part of the v2.0.1 release.

We removed default up-scaling of epsilon (the relative margin allowed) because it silently gave bad results for lowish numbers: ie, it accepted the above comparison even though -0.001 and 0.0 are not within 10% of each other.

[hoisunng]

In my test cases I sometimes even have the case that 1e-20 != Approx(0).
So after this change, what is the suggested way of writing in Catch2, if we want to assert that something is approximately zero?

[horenmar]

Depends on how close to zero you want to be, but for comparisons close to zero the recommended way is
value == Approx(0).margin(allowable_margin).