is this necessary to remove now that the use strict issue is resolved?

So if I add that, then I get:

> ember-cli-code-coverage@0.3.12 lint /Users/paulw/Work/stuff/ember-cli-code-coverage
> eslint config lib test tests *.js


/Users/paulw/.../ember-cli-code-coverage/config/environment.js
  2:1  error  'use strict' is unnecessary inside of modules  strict

/Users/paulw/.../ember-cli-code-coverage/config/release.js
  1:1  error  'use strict' is unnecessary inside of modules  strict

/Users/paulw/.../ember-cli-code-coverage/lib/attach-middleware.js
  1:1  error  'use strict' is unnecessary inside of modules  strict

....

So which do you want, do you want the eslint rule or do you want the "use stricts"? Personally I'd rather have it hue closer to the default ember-cli blueprint, but that's just my opinion.

I think the way you have it now is good

Do you need to protect against prototype members here? (hasOwnProperty)

This is normally going to be a simple array, but I can do it just to be absolutely safe.

I think we are safe here, because this is using "for...of" rather than "for...in". "for...of" only iterates over the elements of the collection:

Object.prototype.objCustom = function() {}; 
Array.prototype.arrCustom = function() {};

let iterable = [3, 5, 7];
iterable.foo = 'hello';

for (let i in iterable) {
  console.log(i); // logs 0, 1, 2, "foo", "arrCustom", "objCustom"
}

for (let i of iterable) {
  console.log(i); // logs 3, 5, 7
}

I missed that, Looks good.