Help representing a concept graphically: Testing pyramid

I have to represent a coding concept called the testing pyramid, more info here:

https://martinfowler.com/articles/practical-test-pyramid.html

This is the image I'm trying to create:

https://martinfowler.com/articles/practical-test-pyramid/testPyramid.png

What I want to try to figure out is how to represent the arrows on either side graphically. It's a challenge because they represent two different things, but are linked.

First arrow: represents how realistic the tests are, i.e. how close it will be to when the code is complete

Second arrow: how fast the tests are to run.

So the more realistic, the slower the test, the less realistic the faster the test.

I was wondering if there was a way to represent this previous sentence graphically. I was thinking of using colors on the pyramid itself or using symbols, but I can't find a good, clear, understandable solution. Graphics that are often used for realism are the planet or cloud. For speed: rabbit, turtle, clock. None of these are great.

TLDR how do I represent a scale of both speed and realism within a single pyramid graphic?

Great design resource

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