Yes Kent is correct however when doing the bend test the coupon or sample is not otherwise reduced in size. There are as many ways to test a weld as there are welding applications and types of welds. Both destructive and non destructive testing procedures are preformed for the fabrication of anything joined by a welding process. the destructive methods are for qualifying a welder the non destruction methods are for the finished weldements.
I like an impact method for single sided but and fillet welds as well as simple bend resistance for impact just weld 2 pieces together either butted at the ends of positioned as a "T" make the appropriate weld to 1 side only then secure one of the pieces so it cannot move then slam it with a hammer from the opposite side to the weld if it bends keep slamming it until it folds onto itself. Then slice it open providing it did not break and examine the grain structure of the weld and heat effected zone. Other ways slightly more scientific is to use a hydraulic press with a pressure gage this will tell you at which point the weld begins to fail.
There is also a test called the nick test. where you make your sample according to the recommended welding fabrication procedure plane the sample on both sides then saw into coupons after saw a nick into the weld on one end of the exposed weld place the coupon on 2 supports with the nick down press from directly above When the weld begins to tear the test has reached the point of failure note the pressure then calculate the square of the weld (thickness and length) multiplied by the actual pressure of the ram area of the press exerted on the test sample this will give you a good indication of the tensile strength of the weld as well only this test can give a false reading if the length of the weld is significantly more than the thickness.
Another quite simple test is to clamp the sample in a vice then fit a socket over it and use a torque wrench to twist the sample until the weld fails. All of the above tests are done with samples having a relatively flat surface segments of pipe may be used as long as they are proportional in size to the diameter of the pipe. usually 1/10th to 1/6th the diameter or 2" wide which ever is less.