APA FORMAT 300 words REFERENCES AND CITATIONS  What is meant by “Test Coverage”

APA FORMAT 300 words REFERENCES AND CITATIONS 
What is meant by “Test Coverage”

APA FORMAT 300 words REFERENCES AND CITATIONS 
What is meant by “Test Coverage”?   Is it usually “impossible” to test all possible combinations of input values in order to guarantee some code is correct?  Or is it possible to test all combinations?  What is practical?