and each of the nine 3x3 sub-grids (also known as blocks) contain all of the digits from 1 to 9.

Because of that.

Expected 'false' on input of < pre>1 2 3 4 5 6 7 8 9|
|2 3 1 5 6 4 8 9 7|
|3 1 2 6 4 5 9 7 8|
|4 5 6 7 8 9 1 2 3|
|5 6 4 8 9 7 2 3 1|
|6 4 5 9 7 8 3 1 2|
|7 8 9 1 2 3 4 5 6|
|8 9 7 2 3 1 5 6 4|
|9 7 8 3 1 2 6 4 5|< /pre>: expected true to equal false

It's should return true... but why false?