I have two companies, both owned by the same four owners in the same percentages. It is definitley a controlled group. They were set up with two separate plans which are identical and only have a 401(k) feature.

Don't I automatically pass coverage since there is only 401(k) and everyone who is eligible is considered 'benefiting' and so I can perform ADP/ACP Testing separately for each plan?

when you have a controlled group, you have all employees under 1 employer.
You have the option of permissively aggregating the plan (assuming they have the same plan year)

if you choose NOT to aggregate plan then you have
Plan A (for coverage Plan B employees are includable and not benefiting) (for ADP test, plan B employees do not show)
Plan B (for coverage Plan A employees are includable and not benefiting) (for ADP test, plan A employees do not show)
[you have to be consistent, if you test coverage seperately, you have to ADP test seperately)

if you aggreagte plans
you are correct, everyone is includable and benefiting, you have 1 ADP test including all employees.

Don't forget that if any HCE's are eligible under both plans, you will have to count their combined deferrals and match in both plans when you test separately. See 1.401(k)-2(a)(3)(ii) & 1.401(m)-2(a)(3)(ii).

As Tom [aka, Pilgrim] points out, even though everyone is eligible for the 401(k) feature and the plans are identical, each plan still must pass 410(b) separately in order for ADP testing to be performed separately. However, if you must aggregate the plans in order for one (or both) of the plans to pass coverage, then you must perform a single ADP test.