Full-stack tests will have a combinatorial explosion in the number of tests you have to write to get decent coverage, wheras isolated unit tests have a linear (with some constants) increase.
Also full stack acceptance tests take ages to run (by definition they will be doing some complex computation). As mentioned above, if their test suite runs in under 5s, it gives a huge advantage. Imagine having light on your computer that goes red any time you make a mistake. They effectively have that.
Also full stack acceptance tests take ages to run (by definition they will be doing some complex computation). As mentioned above, if their test suite runs in under 5s, it gives a huge advantage. Imagine having light on your computer that goes red any time you make a mistake. They effectively have that.