The bug

The title may not be the most accurate description, or imply the best way to fix this. Here's my motivation:

In 1.12.2, you were able to print the block id and data value of a certain block into chat by using /testforblock with a different block id, and then with a different data value, on it. This was very useful for investigating client/server desync bugs (or features...), and I'm sure there are other use cases. The 1.13 equivalent of /testforblock, /execute if block, doesn't print such feedback into chat anymore.

To fix this issue, /execute if block could be given some appropriate chat output. If this is deemed to not be in the spirit of /execute, I suggest adding block id and block state output to /data get block.

Reproduction steps

1. Place a snow layer at your location

   /setblock ~ ~ ~ snow[layers=1]
   

2. Use /execute if block

   /execute if block ~ ~ ~ snow[layers=5]
   

   It only says "Test failed", expected would be something like: "Test failed, found minecraft:snow[layers=1] instead of the expected block" (possibly also including the expected block and coordinates)