Question bank
A full-length test tells you your score. It is much worse at telling you why. The question bank is the other half: pick one section, one topic, one difficulty band, and work through it until the pattern is obvious rather than until the test is over.
SAT
9,000
questions, filterable by section and difficulty
GMAT
questions, filterable by section and difficulty
GRE
questions, filterable by section and difficulty
PTE Academic
questions, filterable by section and difficulty
One topic at a time
Filter to the thing that is going wrong. Twenty questions on one narrow skill teaches you more than a mixed set of two hundred, because you can see what the wrong answers have in common.
Solved questions are remembered
What you have answered is tracked, so a session does not hand you back the questions you already got right. Time spent re-confirming what you know is the most common way people waste a bank this size.
Once a topic stops costing you marks, check whether it holds up under a clock: full-length practice tests.