Thyroid function is tested by drawing blood for levels of TSH (thyroid stimulating hormone), T3 and If your level is higher than normal range than you are hypothyroid. If the level is lower than the normal range you are hyperthyroid.

Addison's is primary diagnosed by drawing early morning fasting levels of your ACTH. If the levels are higher than range they will also draw some additional hormone blood tests but that was the test they used to diagnose me

I have had hyperthyroid for years, now I am hypothyroid. It is easy to test through a blood test.