*info_outline*

Solutions will be available when this assignment is resolved, or after a few failing attempts.

# Identity Matrix

An identity matrix is defined in the following way:

Basically, all the elements in the diagonal are ones (`1`

s) and the rest are zeros (`0`

s).

An identity matrix has a `size`

associated. For example, this is an identity matrix of size 3:

```
1 0 0
0 1 0
0 0 1
```

And this is a matrix of size 5:

```
1 0 0 0 0
0 1 0 0 0
0 0 1 0 0
0 0 0 1 0
0 0 0 0 1
```

A matrix is represented, Pythonically, with a "list of lists". Example:

```
# size 3
size_3_matrix = [
[1, 0, 0],
[0, 1, 0],
[0, 0, 1],
]
# size 5
size_5_matrix = [
[1, 0, 0, 0, 0],
[0, 1, 0, 0, 0],
[0, 0, 1, 0, 0],
[0, 0, 0, 1, 0],
[0, 0, 0, 0, 1],
]
```

Write a function `identity_matrix`

that receives a `size`

parameter and builds an identity matrix using "lists of lists".

### Test Cases

test size 5 identity matrix - Run Test

```
size_5_matrix = [
[1, 0, 0, 0, 0],
[0, 1, 0, 0, 0],
[0, 0, 1, 0, 0],
[0, 0, 0, 1, 0],
[0, 0, 0, 0, 1],
]
def test_size_5_identity_matrix():
assert identity_matrix(5) == size_5_matrix
```

test size 2 identity matrix - Run Test

```
size_2_matrix = [
[1, 0],
[0, 1],
]
def test_size_2_identity_matrix():
assert identity_matrix(2) == size_2_matrix
```

test size 3 identity matrix - Run Test

```
size_3_matrix = [
[1, 0, 0],
[0, 1, 0],
[0, 0, 1],
]
def test_size_3_identity_matrix():
assert identity_matrix(3) == size_3_matrix
```