Delete all of the code from testInstallation.py and instead replace it with an

import of the new testInstallation module and a command to run the tests.

This way, we only have one place where we need to maintain this code, yet the
current workflow of "run testInstallation.py" still works.

examples/testInstallation.py

 from __future__ import print_function
 # First make sure OpenMM is installed.
 
+from simtk import testInstallation
 
-import sys
-try:
-    from simtk.openmm.app import *
-    from simtk.openmm import *
-    from simtk.unit import *
-except ImportError as err:
-    print("Failed to import OpenMM packages:", err.message)
-    print("Make sure OpenMM is installed and the library path is set correctly.")
-    sys.exit()
-
-# Create a System for the tests.
-
-pdb = PDBFile('input.pdb')
-forcefield = ForceField('amber99sb.xml', 'tip3p.xml')
-system = forcefield.createSystem(pdb.topology, nonbondedMethod=PME, nonbondedCutoff=1*nanometer, constraints=HBonds)
-
-# List all installed platforms and compute forces with each one.
-
-numPlatforms = Platform.getNumPlatforms()
-print("There are", numPlatforms, "Platforms available:")
-print()
-forces = [None]*numPlatforms
-platformErrors = {}
-for i in range(numPlatforms):
-    platform = Platform.getPlatform(i)
-    print(i+1, platform.getName(), end=" ")
-    integrator = LangevinIntegrator(300*kelvin, 1/picosecond, 0.002*picoseconds)
-    try:
-        simulation = Simulation(pdb.topology, system, integrator, platform)
-        simulation.context.setPositions(pdb.positions)
-        forces[i] = simulation.context.getState(getForces=True).getForces()
-        del simulation
-        print("- Successfully computed forces")
-    except:
-        print("- Error computing forces with", platform.getName(), "platform")
-        platformErrors[platform.getName()] = sys.exc_info()[1]
-
-# Give details of any errors.
-
-for platform in platformErrors:
-    print()
-    print("%s platform error: %s" % (platform, platformErrors[platform]))
-
-# See how well the platforms agree.
-
-if numPlatforms > 1:
-    print()
-    print("Median difference in forces between platforms:")
-    print()
-    for i in range(numPlatforms):
-        for j in range(i):
-            if forces[i] is not None and forces[j] is not None:
-                errors = []
-                for f1, f2 in zip(forces[i], forces[j]):
-                    d = f1-f2
-                    error = sqrt((d[0]*d[0]+d[1]*d[1]+d[2]*d[2])/(f1[0]*f1[0]+f1[1]*f1[1]+f1[2]*f1[2]))
-                    errors.append(error)
-                print("{} vs. {}: {:g}".format(Platform.getPlatform(j).getName(),
-                                              Platform.getPlatform(i).getName(),
-                                              sorted(errors)[len(errors)//2]))
+testInstallation.run_tests()