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    * CS licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
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    *
    *   http://www.apache.org/licenses/LICENSE-2.0
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   * Unless required by applicable law or agreed to in writing, software
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  package org.orekit.estimation.measurements.modifiers;
  
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.junit.Assert;
  import org.junit.Before;
  import org.junit.Test;
  import org.orekit.Utils;
  import org.orekit.estimation.measurements.EstimatedMeasurement;
  import org.orekit.estimation.measurements.EstimationModifier;
  import org.orekit.estimation.measurements.ObservableSatellite;
  import org.orekit.estimation.measurements.gnss.InterSatellitesPhase;
  import org.orekit.gnss.Frequency;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.analytical.tle.TLE;
  import org.orekit.propagation.analytical.tle.TLEPropagator;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.TimeScalesFactory;
  
  public class RelativisticClockInterSatellitesPhaseModifierTest {
  
      /** Date. */
      private static AbsoluteDate date;
  
      /** Spacecraft states. */
      private static SpacecraftState[] states;
  
      @Test
      public void testRelativisticClockCorrection() {
  
          // Measurement
          final double wavelength = Frequency.G01.getWavelength();
          final InterSatellitesPhase phase = new InterSatellitesPhase(new ObservableSatellite(0), new ObservableSatellite(1),
                                                                      date,
                                                                      Vector3D.distance(states[0].getPVCoordinates().getPosition(),
                                                                                        states[1].getPVCoordinates().getPosition()) / wavelength,
                                                                      wavelength, 1.0, 1.0);
  
          // Inter-satellites phase before applying the modifier
          final EstimatedMeasurement<InterSatellitesPhase> estimatedBefore = phase.estimate(0, 0, states);
  
          // Inter-satellites phase after applying the modifier
          final EstimationModifier<InterSatellitesPhase> modifier = new RelativisticClockInterSatellitesPhaseModifier();
          phase.addModifier(modifier);
          final EstimatedMeasurement<InterSatellitesPhase> estimatedAfter = phase.estimate(0, 0, states);
  
          // Verify
          Assert.assertEquals(-10.57, (estimatedBefore.getEstimatedValue()[0] - estimatedAfter.getEstimatedValue()[0]) * wavelength, 1.0e-2);
          Assert.assertEquals(0, modifier.getParametersDrivers().size());
  
      }
  
      @Before
      public void setUp() {
          // Data root
          Utils.setDataRoot("regular-data");
  
          // Date
          date = new AbsoluteDate("2004-01-13T00:00:00.000", TimeScalesFactory.getUTC());
  
          // Spacecraft states
          states = new SpacecraftState[2];
          final TLE local = new TLE("1 27642U 03002A   04013.91734903  .00000108  00000-0  12227-4 0  3621",
                                    "2 27642  93.9970   6.8623 0003169  80.1383 280.0205 14.90871424 54508");
          final TLE remote = new TLE("1 20061U 89044A   04013.44391333  .00000095  00000-0  10000-3 0  3242",
                                     "2 20061  53.4233 172.2072 0234017 261.4179  95.8975  2.00577231106949");
          states[0] = TLEPropagator.selectExtrapolator(local).propagate(date);
          states[1] = TLEPropagator.selectExtrapolator(remote).propagate(date);
      }
  
  }