Compound Assignment with Augmented Addition allows unintended solution

[robinmetral]

Describe the bug

The Basic Javascript challenge "Compound Assignment with Augmented Addition" basically asks learners to change:
a = a += 12;
to:
a += 12;

However the testing also allows for this solution:
a = a += 12
(which is the one I used because it's quicker to simply add an = sign)

Shouldn't it return an error for this? It should be clear that this compound assignment is intended to remove the first = sign and simplify the code.

Note: this also applies to the three subsequent compound assignment challenges

To Reproduce

Steps to reproduce the behavior:

1. Go to Compound Assignment with Augmented Addition
2. Solve the challenge with this code:

a = a += 12;
b = b += 9;
c = c += 7;

3. See that the tests pass

Expected behavior

Tests to fail.

Desktop (please complete the following information):

• OS: Ubuntu
• Browser: Firefox
• Version 61.0.1