Tests for command `DEL`

[arpitbbhayani]

Currently, there are almost no unit tests for the DEL command. We need a comprehensive test suite for this command that also checks the correctness and completeness.

1. covers the correctness of single command
2. covers the correctness when multiple commands are fired
3. no commands are dropped abruptly
4. ensure we check for small, large, and massive inputs (if applicable)

[rawris]

I can pick this up @arpitbbhayani