## What's wrong in the test?

What’s wrong in the test of `pow`

below?

```
it("Raises x to the power n", function() {
let x = 5;
let result = x;
assert.equal(pow(x, 1), result);
result *= x;
assert.equal(pow(x, 2), result);
result *= x;
assert.equal(pow(x, 3), result);
});
```

P.S. Syntactically the test is correct and passes.

The test demonstrates one of the temptations a developer meets when writing tests.

What we have here is actually 3 tests, but layed out as a single function with 3 asserts.

Sometimes it’s easier to write this way, but if an error occurs, it’s much less obvious what went wrong.

If an error happens inside a complex execution flow, then we’ll have to figure out the data at that point. We’ll actually have to *debug the test*.

It would be much better to break the test into multiple `it`

blocks with clearly written inputs and outputs.

Like this:

```
describe("Raises x to power n", function() {
it("5 in the power of 1 equals 5", function() {
assert.equal(pow(5, 1), 5);
});
it("5 in the power of 2 equals 25", function() {
assert.equal(pow(5, 2), 25);
});
it("5 in the power of 3 equals 125", function() {
assert.equal(pow(5, 3), 125);
});
});
```

We replaced the single `it`

with `describe`

and a group of `it`

blocks. Now if something fails we would see clearly what the data was.

Also we can isolate a single test and run it in standalone mode by writing `it.only`

instead of `it`

:

```
describe("Raises x to power n", function() {
it("5 in the power of 1 equals 5", function() {
assert.equal(pow(5, 1), 5);
});
// Mocha will run only this block
it.only("5 in the power of 2 equals 25", function() {
assert.equal(pow(5, 2), 25);
});
it("5 in the power of 3 equals 125", function() {
assert.equal(pow(5, 3), 125);
});
});
```