Here is a good way to figure all these things out.
If you look around for ESR meter circuits you can find a few with explanations of how they work. There is no one circuit that is superior, but there are circuits that have desirable features like in circuit testing, input protection, auto discharging, audible alert, digital display, multiple frequency support.
As mentioned ideally you want to reproduce the datasheet test as close as possible, which happens to be on an expensive bench meter. The good thing is when electrolytics are going "out of tolerance" on ESR it's really obvious and the ESR reading can be many multiples greater than a new or "in spec" capacitor, so even inexpensive circuits are useful.
Checking the ESR is only one factor in determining a capacitor falling out of spec, and each capacitor brand, series, capacity, voltage etc will have it's own ESR specification on it's datasheet. A capacitance, ESR and visual check will normally weed out any bad ones so capacitance by itself can be misleading.
Reading test equipment operation and service manuals from good vendors will uncover reliable information on how these measurements are made and service manuals specifically have flow diagrams and explain operation. HP in addition to their manuals put out journals which digs deeper into various technologies.
http://assets.fluke.com/manuals/PM6303A_umeng0200.pdfhttp://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/hpjindex.htmlIf you haven't seen it yet, check this video by w2aew.