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  package org.orekit.propagation.semianalytical.dsst.forces;
  
  import org.hipparchus.util.FastMath;
  import org.junit.jupiter.api.Assertions;
  import org.junit.jupiter.api.BeforeEach;
  import org.junit.jupiter.api.Test;
  import org.orekit.Utils;
  import org.orekit.frames.Frame;
  import org.orekit.frames.FramesFactory;
  import org.orekit.orbits.EquinoctialOrbit;
  import org.orekit.orbits.PositionAngleType;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.semianalytical.dsst.utilities.AuxiliaryElements;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.TimeScalesFactory;
  
  import java.io.IOException;
  import java.text.ParseException;
  import java.util.Arrays;
  
  class DSSTNewtonianAttractionTest {
  
      private static final double eps  = 1.0e-19;
  
      @Test
      void testGetMeanElementRate() throws IllegalArgumentException {
  
          final Frame earthFrame = FramesFactory.getEME2000();
  
          final AbsoluteDate date = new AbsoluteDate(2007, 04, 16, 0, 46, 42.400, TimeScalesFactory.getUTC());
  
          final double mu = 3.986004415E14;
          final EquinoctialOrbit orbit = new EquinoctialOrbit(2.655989E7,
                                                              2.719455286199036E-4,
                                                              0.0041543085910249414,
                                                              -0.3412974060023717,
                                                              0.3960084733107685,
                                                              FastMath.toRadians(44.2377),
                                                              PositionAngleType.MEAN,
                                                              earthFrame,
                                                              date,
                                                              mu);
  
          final SpacecraftState state = new SpacecraftState(orbit);
  
          final AuxiliaryElements auxiliaryElements = new AuxiliaryElements(state.getOrbit(), 1);
  
          final DSSTForceModel newton = new DSSTNewtonianAttraction(mu);
  
          final double[] elements = new double[7];
          Arrays.fill(elements, 0.0);
  
          final double[] daidt = newton.getMeanElementRate(state, auxiliaryElements, newton.getParameters());
  
          for (int i = 0; i < daidt.length; i++) {
              elements[i] = daidt[i];
          }
  
          Assertions.assertEquals(0.0,                   elements[0], eps);
          Assertions.assertEquals(0.0,                   elements[1], eps);
          Assertions.assertEquals(0.0,                   elements[2], eps);
          Assertions.assertEquals(0.0,                   elements[3], eps);
          Assertions.assertEquals(0.0,                   elements[4], eps);
          Assertions.assertEquals(1.4585773985530907E-4, elements[5], eps);
  
      }
  
      @BeforeEach
      public void setUp() throws IOException, ParseException {
          Utils.setDataRoot("regular-data");
      }
  
  }