How to create a 2000 Amp load from 500 Amp Power Supply?
Car batteries are rated by the sustained current from full charge at 12.5V to 7.5V or a 5V drop at low temp to yield a cold cranking amperage CCA rating to start cold engines which have more friction.

If a Battery has a CCA rating of 750A at 0'C, it will be higher CCA with temperature due to battery chemistry. 


This 750 CCA battery has equivalent ESR = 5V(drop)/CCA(rise)
To perform a current surge test at low voltage, it makes no different if the voltage is 12 V or 7.5V on the switch equivalent ESR and resulting power dissipation which results in a high temperature rise in 1 second. This will be a value in Joules per second or Watts and the ESR of the switch will result in a measureable Tjcn rise which then translates into an accelerated aging MTBF value that may be researched and calculated as to how many such surges can be performed in it's life time.


As in any electronics or mechanical switch, for low loss and high efficiency, we use conservative values and opt for a ratio of switch ESR or RdsOn or Rce to load resistance such that we desire ESR/R(load) &lt; 2% 
This translates into the voltage drop (I*ESR) and the power drop (I^2*ESR) both a linear proportion with ESR



Conclusion


You only need ; 


a battery bank with a cumulative CCA >> 2000A. (3 car batteries)
50 mV current shunt at 2000A or a suitable ammeter


it must dissipate 100W in 1 sec. (many shunt wires of Nichrome )
signal wires must be shielded with twisted pairs 
the sense wires must be coming off at 90deg to reduce induction
it could be on ground side to read full scale current of 2000A 

a calibrated load to yield 2000A at 8 to 10V or 20kW of heat 


such as many shunts of nichrome wire in water (NiCr 10x better tempco than copper.)

**edit*  Test Phase 2 Inductive load test
since we know the inertia of motors translates into stored energy as a generator, we must consider not just the initial load current but the stored inductive energy and mechanical inertia of the motor now acting as a generator with an contact arc that is sustained until the arc is quenched similar to the holding current threshold of an SCR.
so the test results of a resistive load are far better than a switched inductive DC load and the stored energy in that load.
thus the surge current load test must define this stored inductive and rotational stored energy as part of test #2 
although Relays often rate contact currents for Inductive AC and DC loads much lower than Resistive loads
define your real target loads by Inductance and Rotational stored energy then measure contact temp rise and get a spec for contact max temp rise as a test criteria... ( more later)


  I have used this basic method to monitor currents greater than 100,000 A  with Voc&lt;5V (no load) for Zirc/Steel diffusion bonding machines when I was at Bristol Aerospace Canada in Winnipeg. Zirconium shims were the interface material of choice for welding two Monel Steel 4" tubes together for Nuclear Reactor steam. There were a lot of fireworks in the welding process with forced water spray cooling and the current had to be increased as the pipes were rotated between two solid copper wheels (Inner and Outer) acting as rolling pressure contact as inner steel tube was inserted to another and rolled between the 2 solid copper wheels carrying the current. The weld naturally lowers the ESR of the joint as the shunt resistance drops as it rotated in welded circumferential resistance. **




This high current resistance weld, called "diffusion bonding". ~1979 

more Opinions 

What may  happen to your switch makes contact may be less important than when it breaks contact with the arc power generated by the stored energy in an inductive motor generator load. SO an inductive load will ALWAYS BE more damaging than a Resistive load of sparks until the >>5000'K heat burns off the surface oxidize creates a lower contact resistance by melting impurities. 

What happens during long term exposures  (I*t) and the thermal properties of the metal alloy contacts is a matter of great research in chemistry and physics of higher temperature exotic metal alloys. If you are new to this look at the contact materials used by companies like OMRON that use the best metal alloys for the contacts required.