Given a set of words, find the longest chain of words that can be made out of those words with the following rules:

• Each word in the chain is one letter longer than the previous word.

• Each word in the chain differs from the previous word only by its last letter.

Write test case's. Also, mention the Time and Space complexity for the same.

Constraint Examples: 

den -> dent-> dents is valid (meets all constraints) 

den -> dew is not valid (same length: 3 characters) 

den -> cent is not valid (differs by 1’st char [‘d’ != ‘c’]) 

Example:

Input: {ben, bent, dew, dents, dent, bet, den}

Output: 3 ({den, dent, dents})