''' '''
'''
 ISC License
 Copyright (c) 2016, Autonomous Vehicle Systems Lab, University of Colorado at Boulder
 Permission to use, copy, modify, and/or distribute this software for any
 purpose with or without fee is hereby granted, provided that the above
 copyright notice and this permission notice appear in all copies.
 THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
'''
import os, inspect
import math
import numpy as np
filename = inspect.getframeinfo(inspect.currentframe()).filename
path = os.path.dirname(os.path.abspath(filename))
from Basilisk import __path__
bskPath = __path__[0]
from Basilisk.utilities import SimulationBaseClass
from Basilisk.utilities import unitTestSupport  # general support file with common unit test functions
from Basilisk.utilities import macros
from Basilisk.simulation import gravityEffector
from Basilisk.simulation import spice_interface
from Basilisk import pyswice
from Basilisk.simulation import stateArchitecture
from Basilisk.simulation.gravityEffector.gravCoeffOps import loadGravFromFileToList
from Basilisk.utilities import orbitalMotion as om
from Basilisk.simulation import simMessages
#script to check spherical harmonics calcs out to 20th degree
#Uses coefficient from Vallado tables D-1
def computeGravityTo20(positionVector):
    #This code follows the formulation in Vallado, page 521, second edition and uses data from UTexas CSR for
    #gravitation harmonics parameters
    #Written 201780807 by Scott Carnahan
    #AVS Lab | CU Boulder
    #INPUTS
    #positionVector - [x,y,z] coordinates list of spacecraft in [m] in earth body frame so that lat, long can be calculated
    def legendres(degree, alpha):
        P = np.zeros((degree+1,degree+1))
        P[0,0] = 1
        P[1,0] = alpha
        cosPhi = np.sqrt(1-alpha**2)
        P[1,1] = cosPhi
        for l in range(2,degree+1):
            for m in range(0,l+1):
                if m == 0 and l >= 2:
                    P[l,m] = ((2*l-1)*alpha*P[l-1,0]-(l-1)*P[l-2,0]) / l
                elif m != 0 and m < l:
                    P[l, m] = (P[l-2, m]+(2*l-1)*cosPhi*P[l-1,m-1])
                elif m == l and l != 0:
                    P[l,m] = (2*l-1)*cosPhi*P[l-1,m-1]
                else:
                    print(l,", ", m)
        return P
    maxDegree = 20
    cList = np.zeros(maxDegree+2)
    sList = np.zeros(maxDegree+2)
    muEarth = 0.
    radEarth = 0.
    [cList, sList, muEarth, radEarth]  = loadGravFromFileToList(path + '/GGM03S.txt', maxDegree+2)
    r = np.linalg.norm(positionVector)
    rHat = positionVector / r
    gHat = rHat
    grav0 = -gHat * muEarth / r**2
    rI = positionVector[0]
    rJ = positionVector[1]
    rK = positionVector[2]
    rIJ = np.sqrt(rI**2 + rJ**2)
    if rIJ != 0.:
        phi = math.atan(rK / rIJ) #latitude in radians
    else:
        phi = math.copysign(np.pi/2., rK)
    if rI != 0.:
        lambdaSat = math.atan(rJ / rI) #longitude in radians
    else:
        lambdaSat = math.copysign(np.pi/2., rJ)
    P = legendres(maxDegree+1,np.sin(phi))
    dUdr = 0.
    dUdphi = 0.
    dUdlambda = 0.
    for l in range(0, maxDegree+1):
        for m in range(0,l+1):
            if m == 0:
                k = 1
            else:
                k = 2
            num = math.factorial(l+m)
            den = math.factorial(l-m)*k*(2*l+1)
            PI = np.sqrt(float(num)/float(den))
            cList[l][m] = cList[l][m] / PI
            sList[l][m] = sList[l][m] / PI
    for l in range(2,maxDegree+1): #can only do for max degree minus 1
        for m in range(0,l+1):
            dUdr = dUdr + (((radEarth/r)**l)*(l+1)*P[l,m]) * (cList[l][m]*np.cos(m*lambdaSat)+sList[l][m]*np.sin(m*lambdaSat))
            dUdphi = dUdphi + (((radEarth/r)**l)*P[l,m+1] - m*np.tan(phi)*P[l,m]) * (cList[l][m]*np.cos(m*lambdaSat) + sList[l][m]*np.sin(m*lambdaSat))
            dUdlambda = dUdlambda + (((radEarth/r)**l)*m*P[l,m]) * (sList[l][m]*np.cos(m*lambdaSat) - cList[l][m]*np.sin(m*lambdaSat))
    dUdr = -muEarth * dUdr / r**2
    dUdphi = muEarth * dUdphi / r
    dUdlambda = muEarth * dUdlambda / r
    if rI != 0. and rJ != 0.:
        accelerationI = (dUdr/r - rK*dUdphi/(r**2)/((rI**2+rJ**2)**0.5))*rI - (dUdlambda/(rI**2+rJ**2))*rJ + grav0[0]
        accelerationJ = (dUdr/r - rK*dUdphi/(r**2)/((rI**2+rJ**2)**0.5))*rJ + (dUdlambda/(rI**2+rJ**2))*rI + grav0[1]
    else:
        accelerationI = dUdr/r + grav0[0]
        accelerationJ = dUdr/r + grav0[1]
    accelerationK = (dUdr/r)*rK + (((rI**2+rJ**2)**0.5)*dUdphi/(r**2)) + grav0[2]
    accelerationVector = [accelerationI, accelerationJ, accelerationK]
    return accelerationVector
# uncomment this line is this test is to be skipped in the global unit test run, adjust message as needed
# @pytest.mark.skipif(conditionstring)
# uncomment this line if this test has an expected failure, adjust message as needed
# @pytest.mark.xfail() # need to update how the RW states are defined
# provide a unique test method name, starting with test_
[docs]def test_gravityEffectorAllTest(show_plots):
    """Module Unit Test"""
    [testResults, testMessage] = independentSphericalHarmonics(show_plots)
    assert testResults < 1, testMessage
    [testResults, testMessage] = sphericalHarmonics(show_plots)
    assert testResults < 1, testMessage
    [testResults, testMessage] = singleGravityBody(show_plots)
    assert testResults < 1, testMessage
    [testResults, testMessage] = multiBodyGravity(show_plots)
    assert testResults < 1, testMessage 
def independentSphericalHarmonics(show_plots):
    testCase = "independentCheck"
    # The __tracebackhide__ setting influences pytest showing of tracebacks:
    # the mrp_steering_tracking() function will not be shown unless the
    # --fulltrace command line option is specified.
    __tracebackhide__ = True
    testFailCount = 0  # zero unit test result counter
    testMessages = []  # create empty list to store test log messages
    spherHarm = gravityEffector.SphericalHarmonics()
    gravityEffector.loadGravFromFile(path + '/GGM03S.txt', spherHarm, 20)
    gravCheck = computeGravityTo20([15000., 10000., 6378.1363E3])
    spherHarm.initializeParameters()
    gravOut = spherHarm.computeField([[15000.0], [10000.0], [(6378.1363) * 1.0E3]], 20, True)
    gravOutMag = np.linalg.norm(gravOut)
    gravCheckMag = np.linalg.norm(gravCheck)
    accuracy = 1e-12
    relative = (gravCheckMag-gravOutMag)/gravCheckMag
    if abs(relative) > accuracy:
        testFailCount += 1
        testMessages.append("Failed independent spherical harmonics check")
    snippetName = testCase + 'Accuracy'
    snippetContent = '{:1.1e}'.format(accuracy)  # write formatted LATEX string to file to be used by auto-documentation.
    unitTestSupport.writeTeXSnippet(snippetName, snippetContent,
                                    path)  # write formatted LATEX string to file to be used by auto-documentation.
    if testFailCount == 0:
        passFailText = 'PASSED'
        print("PASSED: " + testCase)
        colorText = 'ForestGreen'  # color to write auto-documented "PASSED" message in in LATEX.
        snippetName = testCase + 'FailMsg'
        snippetContent = ""
        unitTestSupport.writeTeXSnippet(snippetName, snippetContent,
                                        path)  # write formatted LATEX string to file to be used by auto-documentation.
    else:
        passFailText = 'FAILED'
        colorText = 'Red'  # color to write auto-documented "FAILED" message in in LATEX
        snippetName = testCase + 'FailMsg'
        snippetContent = passFailText
        for message in testMessages:
            snippetContent += ". " + message
        snippetContent += "."
        unitTestSupport.writeTeXSnippet(snippetName, snippetContent,
                                        path)  # write formatted LATEX string to file to be used by auto-documentation.
    snippetName = testCase + 'PassFail'  # name of file to be written for auto-documentation which specifies if this test was passed or failed.
    snippetContent = r'\textcolor{' + colorText + '}{' + passFailText + '}'  # write formatted LATEX string to file to be used by auto-documentation.
    unitTestSupport.writeTeXSnippet(snippetName, snippetContent,
                                    path)  # write formatted LATEX string to file to be used by auto-documentation.
    # return fail count and join into a single string all messages in the list
    # testMessage
    return [testFailCount, ''.join(testMessages)]
def sphericalHarmonics(show_plots):
    testCase = 'sphericalHarmonics'
    # The __tracebackhide__ setting influences pytest showing of tracebacks:
    # the mrp_steering_tracking() function will not be shown unless the
    # --fulltrace command line option is specified.
    __tracebackhide__ = True
    testFailCount = 0  # zero unit test result counter
    testMessages = []  # create empty list to store test log messages
    spherHarm = gravityEffector.SphericalHarmonics()
    testHarm = [[1.0, 0.0, 0.0], [0.0, 1.0, 0.0], [0.0, 0.0, 1.0]]
    spherHarm.cBar = gravityEffector.MultiArray(testHarm)
    vecCheckSuccess = True
    for i in range(len(spherHarm.cBar)):
        for j in range(len(spherHarm.cBar[i])):
            if spherHarm.cBar[i][j] != testHarm[i][j]:
                vecCheckSuccess = False
    if(vecCheckSuccess != True):
        testFailCount += 1
        testMessages.append("2D vector not input appropriately to spherical harmonics")
    gravityEffector.loadGravFromFile(path + '/GGM03S.txt', spherHarm, 20)
    spherHarm.initializeParameters()
    gravOut = spherHarm.computeField([[0.0], [0.0], [(6378.1363)*1.0E3]], 20, True)
    gravMag = np.linalg.norm(np.array(gravOut))
    accuracy = 0.1
    gravExpected = 9.8
    if gravMag > (gravExpected + accuracy) or gravMag < (gravExpected - accuracy):
        testFailCount += 1
        testMessages.append("Gravity magnitude not within allowable tolerance")
    snippetName = testCase + 'Accuracy'
    snippetContent = '{:1.1e}'.format(accuracy)  # write formatted LATEX string to file to be used by auto-documentation.
    unitTestSupport.writeTeXSnippet(snippetName, snippetContent, path) #write formatted LATEX string to file to be used by auto-documentation.
    gravOutMax = spherHarm.computeField([[0.0], [0.0], [(6378.1363)*1.0E3]], 100, True)
    if gravOutMax != gravOut:
        testFailCount += 1
        testMessages.append("Gravity ceiling not enforced correctly")
    if testFailCount == 0:
        passFailText = 'PASSED'
        print("PASSED: " + " Spherical Harmonics")
        colorText = 'ForestGreen'  # color to write auto-documented "PASSED" message in in LATEX.
        snippetName = testCase + 'FailMsg'
        snippetContent = ""
        unitTestSupport.writeTeXSnippet(snippetName, snippetContent, path)  # write formatted LATEX string to file to be used by auto-documentation.
    else:
        passFailText = 'FAILED'
        colorText = 'Red'  # color to write auto-documented "FAILED" message in in LATEX
        snippetName = testCase + 'FailMsg'
        snippetContent = passFailText
        for message in testMessages:
            snippetContent += ". " + message
        snippetContent += "."
        unitTestSupport.writeTeXSnippet(snippetName, snippetContent, path)  # write formatted LATEX string to file to be used by auto-documentation.
    snippetName = testCase + 'PassFail'  # name of file to be written for auto-documentation which specifies if this test was passed or failed.
    snippetContent = r'\textcolor{' + colorText + '}{' + passFailText + '}' #write formatted LATEX string to file to be used by auto-documentation.
    unitTestSupport.writeTeXSnippet(snippetName, snippetContent, path) #write formatted LATEX string to file to be used by auto-documentation.
    # return fail count and join into a single string all messages in the list
    # testMessage
    return [testFailCount, ''.join(testMessages)]
def singleGravityBody(show_plots):
    testCase = 'singleBody'
    # The __tracebackhide__ setting influences pytest showing of tracebacks:
    # the mrp_steering_tracking() function will not be shown unless the
    # --fulltrace command line option is specified.
    __tracebackhide__ = True
    testFailCount = 0  # zero unit test result counter
    testMessages = []  # create empty list to store test log messages
    # Create a sim module as an empty container
    unitTaskName = "unitTask"  # arbitrary name (don't change)
    unitProcessName = "TestProcess"  # arbitrary name (don't change)
    DateSpice = "2015 February 10, 00:00:00.0 TDB"
    # Create a sim module as an empty container
    TotalSim = SimulationBaseClass.SimBaseClass()
    DynUnitTestProc = TotalSim.CreateNewProcess(unitProcessName)
    # create the dynamics task and specify the integration update time
    DynUnitTestProc.addTask(TotalSim.CreateNewTask(unitTaskName, macros.sec2nano(0.1)))
    # Initialize the modules that we are using.
    SpiceObject = spice_interface.SpiceInterface()
    SpiceObject.ModelTag = "SpiceInterfaceData"
    SpiceObject.SPICEDataPath = bskPath + '/supportData/EphemerisData/'
    SpiceObject.outputBufferCount = 10000
    SpiceObject.planetNames = spice_interface.StringVector(["earth", "mars barycenter", "sun"])
    SpiceObject.UTCCalInit = DateSpice
    TotalSim.AddModelToTask(unitTaskName, SpiceObject)
    SpiceObject.UTCCalInit = "1994 JAN 26 00:02:00.184"
    gravBody1 = gravityEffector.GravBodyData()
    gravBody1.bodyInMsgName = "earth_planet_data"
    gravBody1.outputMsgName = "earth_display_frame_data"
    gravBody1.isCentralBody = False
    gravBody1.useSphericalHarmParams = True
    gravityEffector.loadGravFromFile(path + '/GGM03S.txt', gravBody1.spherHarm, 60)
    # Use the python spice utility to load in spacecraft SPICE ephemeris data
    # Note: this following SPICE data only lives in the Python environment, and is
    #       separate from the earlier SPICE setup that was loaded to BSK.  This is why
    #       all required SPICE libraries must be included when setting up and loading
    #       SPICE kernals in Python.
    pyswice.furnsh_c(bskPath + '/supportData/EphemerisData/de430.bsp')
    pyswice.furnsh_c(bskPath + '/supportData/EphemerisData/naif0012.tls')
    pyswice.furnsh_c(bskPath + '/supportData/EphemerisData/de-403-masses.tpc')
    pyswice.furnsh_c(bskPath + '/supportData/EphemerisData/pck00010.tpc')
    pyswice.furnsh_c(path + '/hst_edited.bsp')
    SpiceObject.UTCCalInit = "2012 MAY 1 00:02:00.184"
    stringCurrent = SpiceObject.UTCCalInit
    et = pyswice.new_doubleArray(1)
    dt = 1.0
    pyswice.str2et_c(stringCurrent, et)
    etCurr = pyswice.doubleArray_getitem(et, 0)
    normVec = []
    gravErrNorm = []
    SpiceObject.UTCCalInit = stringCurrent
    TotalSim.InitializeSimulation()
    gravBody1.initBody(0)
    SpiceObject.UpdateState(0)
    for i in range(2*3600):
        stateOut = pyswice.spkRead('HUBBLE SPACE TELESCOPE', stringCurrent, 'J2000', 'EARTH')
        etPrev =etCurr - 2.0
        stringPrev = pyswice.et2utc_c(etPrev, 'C', 4, 1024, "Yo")
        statePrev = pyswice.spkRead('HUBBLE SPACE TELESCOPE', stringPrev, 'J2000', 'EARTH')
        etNext =etCurr + 2.0
        stringNext = pyswice.et2utc_c(etNext, 'C', 4, 1024, "Yo")
        stateNext = pyswice.spkRead('HUBBLE SPACE TELESCOPE', stringNext, 'J2000', 'EARTH')
        gravVec = (stateNext[3:6] - statePrev[3:6])/(etNext - etPrev)
        normVec.append(np.linalg.norm(stateOut[0:3]))
        stateOut*=1000.0
        SpiceObject.J2000Current = etCurr;SpiceObject.UpdateState(0)
        gravBody1.loadEphemeris(0)
        gravOut = gravBody1.computeGravityInertial(stateOut[0:3].reshape(3,1).tolist(), 0)
        gravErrNorm.append(np.linalg.norm(gravVec*1000.0 - np.array(gravOut).reshape(3))/
            np.linalg.norm(gravVec*1000.0))
        pyswice.str2et_c(stringCurrent, et)
        etCurr = pyswice.doubleArray_getitem(et, 0)
        etCurr += dt;
        stringCurrent = pyswice.et2utc_c(etCurr, 'C', 4, 1024, "Yo")
    accuracy = 1.0e-4
    for gravErr in gravErrNorm:
        if gravErr > accuracy:
            testFailCount += 1
            testMessages.append("Gravity numerical error too high for kernel comparison")
            break
    snippetName = testCase + 'Accuracy'
    snippetContent = '{:1.1e}'.format(accuracy)  # write formatted LATEX string to file to be used by auto-documentation.
    unitTestSupport.writeTeXSnippet(snippetName, snippetContent, path) #write formatted LATEX string to file to be used by auto-documentation.
    pyswice.unload_c(bskPath + '/supportData/EphemerisData/de430.bsp')
    pyswice.unload_c(bskPath + '/supportData/EphemerisData/naif0012.tls')
    pyswice.unload_c(bskPath + '/supportData/EphemerisData/de-403-masses.tpc')
    pyswice.unload_c(bskPath + '/supportData/EphemerisData/pck00010.tpc')
    pyswice.unload_c(path + '/hst_edited.bsp')
    if testFailCount == 0:
        passFailText = 'PASSED'
        print("PASSED: " + "Single-body with Spherical Harmonics")
        colorText = 'ForestGreen'  # color to write auto-documented "PASSED" message in in LATEX
        snippetName = testCase + 'FailMsg'
        snippetContent = ""
        unitTestSupport.writeTeXSnippet(snippetName, snippetContent, path)  # write formatted LATEX string to file to be used by auto-documentation.
    else:
        passFailText = 'FAILED'
        colorText = 'Red'  # color to write auto-documented "FAILED" message in in LATEX
        snippetName = testCase + 'FailMsg'
        snippetContent = passFailText
        for message in testMessages:
            snippetContent += ". " + message
        snippetContent += "."
        unitTestSupport.writeTeXSnippet(snippetName, snippetContent, path)  # write formatted LATEX string to file to be used by auto-documentation.
    snippetName = testCase + 'PassFail'  # name of file to be written for auto-documentation which specifies if this test was passed or failed.
    snippetContent = r'\textcolor{' + colorText + '}{' + passFailText + '}' #write formatted LATEX string to file to be used by auto-documentation.
    unitTestSupport.writeTeXSnippet(snippetName, snippetContent, path) #write formatted LATEX string to file to be used by auto-documentation.
    # return fail count and join into a single string all messages in the list
    # testMessage
    return [testFailCount, ''.join(testMessages)]
def multiBodyGravity(show_plots):
    testCase = 'multiBody' #for AutoTeX stuff
    # The __tracebackhide__ setting influences pytest showing of tracebacks:
    # the mrp_steering_tracking() function will not be shown unless the
    # --fulltrace command line option is specified.
    __tracebackhide__ = True
    testFailCount = 0  # zero unit test result counter
    testMessages = []  # create empty list to store test log messages
    #
    # # Create a sim module as an empty container
    unitTaskName = "unitTask"  # arbitrary name (don't change)
    unitProcessName = "TestProcess"  # arbitrary name (don't change)
    # DateSpice = "2015 February 10, 00:00:00.0 TDB"
    #
    # # Create a sim module as an empty container
    multiSim = SimulationBaseClass.SimBaseClass()
    #
    DynUnitTestProc = multiSim.CreateNewProcess(unitProcessName)
    # # create the dynamics task and specify the integration update time
    DynUnitTestProc.addTask(multiSim.CreateNewTask(unitTaskName, macros.sec2nano(1000.0)))
    #Create dynParamManager to feed fake spacecraft data to so that the gravityEffector can access it.
    #This places the spacecraft at the coordinate frame origin so that planets can be placed around it.
    #velocity and attitude are just set to zero.
    #center of mass and time are set to zero.
    newManager = stateArchitecture.DynParamManager()
    positionName = "hubPosition"
    stateDim = [3, 1]
    posState = newManager.registerState(stateDim[0], stateDim[1], positionName)
    posVelSig = [[0.],[0.],[0.]]
    posState.setState(posVelSig)
    velocityName = "hubVelocity"
    stateDim = [3, 1]
    velState = newManager.registerState(stateDim[0], stateDim[1], velocityName)
    velState.setState(posVelSig)
    sigmaName = "hubSigma"
    stateDim = [3, 1]
    sigmaState = newManager.registerState(stateDim[0], stateDim[1], sigmaName)
    sigmaState.setState(posVelSig)
    initC_B = [[0.0], [0.0], [0.0]]
    newManager.createProperty("centerOfMassSC", initC_B)
    newManager.createProperty("systemTime", [[0], [0.0]])
    #
    #Create a message struct to place gravBody1 where it is wanted
    localPlanetEditor = simMessages.SpicePlanetStateSimMsg()
    localPlanetEditor.PositionVector = [om.AU/10., 0., 0.]
    localPlanetEditor.VelocityVector = [0., 0., 0.]
    #Grav Body 1 is twice the size of the other two
    gravBody1 = gravityEffector.GravBodyData()
    gravBody1.bodyInMsgName = "gravBody1_planet_data"
    gravBody1.outputMsgName = "gravBody1_display_frame_data"
    gravBody1.mu = 1000000.
    gravBody1.radEquator = 6500.
    gravBody1.isCentralBody = False
    gravBody1.useSphericalHarmParams = False
    gravBody1.localPlanet = localPlanetEditor
    #This is the gravityEffector which will actually compute the gravitational acceleration
    allGrav = gravityEffector.GravityEffector()
    allGrav.gravBodies = gravityEffector.GravBodyVector([gravBody1])
    allGrav.linkInStates(newManager)
    allGrav.registerProperties(newManager)
    multiSim.AddModelToTask(unitTaskName, allGrav)
    allGrav.computeGravityField(posVelSig,posVelSig) #compute acceleration only considering the first body.
    step1 = newManager.getPropertyReference("g_N") #retrieve total gravitational acceleration in inertial frame
    #Create a message struct to place gravBody2&3 where they are wanted.
    localPlanetEditor.PositionVector = [-om.AU/10., 0., 0.]
    localPlanetEditor.VelocityVector = [0., 0., 0.]
    #grav Body 2 and 3 are coincident with each other, half the mass of gravBody1 and are in the opposite direction of gravBody1
    gravBody2 = gravityEffector.GravBodyData()
    gravBody2.bodyInMsgName = "gravBody2_planet_data"
    gravBody2.outputMsgName = "gravBody2_display_frame_data"
    gravBody2.mu = gravBody1.mu/2.
    gravBody2.radEquator = 6500.
    gravBody2.isCentralBody = False
    gravBody2.useSphericalHarmParams = False
    gravBody2.localPlanet = localPlanetEditor
    #This is the gravityEffector which will actually compute the gravitational acceleration
    allGrav.gravBodies = gravityEffector.GravBodyVector([gravBody1, gravBody2])
    allGrav.computeGravityField(posVelSig,posVelSig) #compute acceleration considering the first and second bodies.
    step2 = newManager.getPropertyReference("g_N") #retrieve total gravitational acceleration in inertial frame
    # grav Body 2 and 3 are coincident with each other, half the mass of gravBody1 and are in the opposite direction of gravBody1
    gravBody3 = gravityEffector.GravBodyData()
    gravBody3.bodyInMsgName = "gravBody3_planet_data"
    gravBody3.outputMsgName = "gravBody3_display_frame_data"
    gravBody3.mu = gravBody2.mu
    gravBody3.radEquator = 6500.
    gravBody3.isCentralBody = False
    gravBody3.useSphericalHarmParams = False
    gravBody3.localPlanet = localPlanetEditor
    #This is the gravityEffector which will actually compute the gravitational acceleration
    allGrav.gravBodies = gravityEffector.GravBodyVector([gravBody1, gravBody2, gravBody3])
    allGrav.computeGravityField(posVelSig,posVelSig) #comput acceleration considering all three bodies
    step3 = newManager.getPropertyReference("g_N") #retrieve total gravitational acceleration in inertial frame
    step3 = [0., step3[0][0], step3[1][0], step3[2][0]] #add a first (time) column to use isArrayZero
    #Test results for accuracy
    accuracy = 1e-12
    snippetName = testCase + 'Accuracy'
    snippetContent = '{:1.1e}'.format(accuracy)  # write formatted LATEX string to file to be used by auto-documentation.
    unitTestSupport.writeTeXSnippet(snippetName, snippetContent, path) #write formatted LATEX string to file to be used by auto-documentation.
    if not unitTestSupport.isDoubleEqualRelative(step2[0][0]/step1[0][0], 0.5, accuracy): #if the second grav body doesn't cancel exactly half of the first body's acceleration.
        testFailCount += 1
        passFailText = "Step 2 was not half of step 1"
        testMessages.append(passFailText)
    elif not unitTestSupport.isArrayZero(step3, 3, accuracy): #if the net acceleration is not now 0.
        testFailCount += 1
        passFailText = "Step 3 did not cause gravity to return to 0"
        testMessages.append(passFailText)
    #Record test results to LaTeX
    if testFailCount == 0:
        passFailText = 'PASSED'
        print("PASSED: " + " Multi-Body")
        colorText = 'ForestGreen'  # color to write auto-documented "PASSED" message in in LATEX
        snippetName = testCase + 'FailMsg'
        snippetContent = ""
        unitTestSupport.writeTeXSnippet(snippetName, snippetContent, path)  # write formatted LATEX string to file to be used by auto-documentation.
    else:
        passFailText = 'FAILED'
        colorText = 'Red'  # color to write auto-documented "FAILED" message in in LATEX
        snippetName = testCase + 'FailMsg'
        snippetContent = passFailText
        for message in testMessages:
            snippetContent += ". " + message
        snippetContent += "."
        unitTestSupport.writeTeXSnippet(snippetName, snippetContent, path)  # write formatted LATEX string to file to be used by auto-documentation.
    snippetName = testCase + 'PassFail'  # name of file to be written for auto-documentation which specifies if this test was passed or failed.
    snippetContent = r'\textcolor{' + colorText + '}{' + passFailText + '}' #write formatted LATEX string to file to be used by auto-documentation.
    unitTestSupport.writeTeXSnippet(snippetName, snippetContent, path) #write formatted LATEX string to file to be used by auto-documentation.
    return [testFailCount, ''.join(testMessages)]
if __name__ == "__main__":
    test_gravityEffectorAllTest(False)