First thought is to tap on the starter housing with a hammer while
someone attempts to crank the vehicle.  If it starts immediately, then
you know the starter is shot.

regarding your testing question:

Using an inductive current meter such as the kind that plug into a
DVOM, you could measure the peak and average current draw of your
starter when cranking.  A high current reading, like above 200 amps,
would point to a bad starter motor winding -- or a serious engine
problem.  You can put a breaker bar on the front crankshaft bolt and
attempt to turn the engine by hand to determine if the engine is
spinning freely.

You could also measure battery voltage while cranking.  If it is
dropping below about 9 volts then the battery should be charged/tested
and replaced if necessary.  Even a shunted starter wouldn't draw a
fresh, fully charged battery down to extremely low voltage for the
first few seconds, so this is a cheap and relatively accurate way to
test your battery without a load pile device.

Replacement:

The starter is held in place with two 9/16" head (I think) bolts.
Disconnect the battery first, then remove the two wires that go to the
solenoid housing, making sure to remember their orientation.  Next,
remove the two large bolts.  You may have to loosen the torque
converter inspection shield if it is in the way of the starter.  GM
uses shims to set the distance between the starter drive gear and the
ring gear teeth.  Read the instruction pamphlet that comes with your
new starter to understand how to select the correct shim.  You should
also get a packet of ~ two shims with the new starter.

Toyota MDT in MO