If an explosion is centered inside of an explosion proof block like bedrock or command block, the explosion will not destroy any blocks. This occurs with both TNT and End Crystals.

To reproduce

1. Stand on a piece of bedrock and enter /summon minecraft:end_crystal ~ ~ ~
2. Place blocks around it that can break upon explosion
3. Punch the end crystal
=> No blocks will be destroyed

Original text

So, the other day when I decided to use a command block for TNT, I entered this input:

/summon tnt

The explosion happened, but nothing was destroyed, and mobs barely took damage from it.