Fix saccade velocity sorting and add tests

I don't actually like this implementation. Future programmer, see the associated issue in the PR for more explanations. I am lost and didn't get a response on what to do from the boss

src/main/java/com/github/thed2lab/analysis/SaccadeVelocity.java

@@ -27,18 +27,24 @@ static public LinkedHashMap<String,String> analyze(DataEntry data) {
                 if (!prevID.equals(currID) && positionProfile.size() != 0) {
                     positionProfiles.add(positionProfile);
                     positionProfile = new ArrayList<Double[]>();
-                    prevID = currID;
                 }
 
                 Double x = Double.parseDouble(data.getValue(FIXATIONX_INDEX, i));
                 Double y = Double.parseDouble(data.getValue(FIXATIONY_INDEX, i));
                 Double t = Double.parseDouble(data.getValue(TIME_INDEX, i));
                 positionProfile.add(new Double[] {x, y, t});
+                prevID = currID;
 
             } else if (positionProfile.size() != 0) {
                 positionProfiles.add(positionProfile);
                 positionProfile = new ArrayList<Double[]>();
             }
+        } 
+
+        // add the last saccade profile if it isn't already added
+        // see issue #39 and #40 for explanation
+        if (positionProfile.size() > 0) {
+            positionProfiles.add(positionProfile); 
         }
 
         for (int i = 0; i < positionProfiles.size(); i++) {
@@ -56,7 +62,7 @@ static public LinkedHashMap<String,String> analyze(DataEntry data) {
     }
 
 
-    /*
+    /**
 	 * Returns the peak velocity of a given saccade calculated using a two point central difference algorithm.
 	 * 
 	 * @param	saccadePoints	A list of saccade data points, where each data point is a double array. 

src/test/java/com/github/thed2lab/analysis/SaccadeVelocityTest.java

@@ -0,0 +1,85 @@
+package com.github.thed2lab.analysis;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.io.File;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.Test;
+
+public class SaccadeVelocityTest {
+
+   final double PRECISION = 0.000000001; // allowable floating point error
+   final static int SCREEN_WIDTH = 1920;
+	final static int SCREEN_HEIGHT = 1080;
+
+   @Test
+   public void testGetPeakVelocity_emptyPoints_returnNaN() {
+      List<Double[]> emptyList = new ArrayList<>();
+      boolean isNaN = Double.isNaN(SaccadeVelocity.getPeakVelocity(emptyList));
+      assertTrue(isNaN);
+   }
+
+   @Test
+   public void testGetPeakVelocity_onePoint_returnNaN() {
+      List<Double[]> onePoint = new ArrayList<>() {{
+         add(new Double[]{1., 1., 0.001});
+      }};
+      boolean isNaN = Double.isNaN(SaccadeVelocity.getPeakVelocity(onePoint));
+      assertTrue(isNaN);
+   }
+
+   @Test
+   public void testGetPeakVelocity_aboveThreshold_return0() {
+      List<Double[]> saccadePoints = new ArrayList<>() {{
+         add(new Double[]{0., 0., 0.});
+         add(new Double[]{0., 10., 0.0001});
+      }};
+      // 2332.21914 > 700 => return 0
+      boolean isZero = SaccadeVelocity.getPeakVelocity(saccadePoints) == 0;
+      assertTrue(isZero);
+   }
+
+   @Test
+   public void testGetPeakVelocity_normalUseCase_returnVelocityValue() {
+
+   }
+
+   @Test
+   public void testSaccadeVelocityAnalyze_nonContinuousEndsWithSaccadeData() {
+      final String GAZE_PATH = "./src/test/resources/filtered_by_validity.csv";
+      final double EXPECTED_AVG_PEAK = 169.15239533934;
+      final String KEY = "average_peak_saccade_velocity";
+      DataEntry gazeData = DataFilter.applyScreenSize(FileHandler.buildDataEntry(new File(GAZE_PATH)), SCREEN_WIDTH, SCREEN_HEIGHT);
+
+      Map<String, String> actualMap = SaccadeVelocity.analyze(gazeData);
+      assertEquals(1, actualMap.size());
+      assertEquals(EXPECTED_AVG_PEAK, Double.parseDouble(actualMap.get(KEY)), PRECISION);
+
+   }
+
+   @Test
+   public void testSaccadeVelocityAnalyze_nonContinuousEndsWithFixationData() {
+      final String GAZE_PATH = "./src/test/resources/filtered_by_validity.csv";
+      final double EXPECTED_AVG_PEAK = 169.15239533934;
+      final String KEY = "average_peak_saccade_velocity";
+      DataEntry gazeData = DataFilter.applyScreenSize(FileHandler.buildDataEntry(new File(GAZE_PATH)), SCREEN_WIDTH, SCREEN_HEIGHT);
+      gazeData.process(Arrays.asList(
+         "0","X-Plane","971","6.53005","5.88E+12","0.47815","0.45335",
+         "6.53005","0.14856","25","1","0.46056","0.45713","1","0.60729",
+         "0.47315","0"," ","0","","0.41066","0.36362","16.25439","1.08789",
+         "1","0.61855","0.37037","15.69818","1.08789","1","0","0","11",
+         "4.43149","1","4.03482","1","0","0","0","0","0","0","0","0","1",
+         "1","1","1","1","1","1","0","0","0","AOI_A","0","0","0"
+      ));
+
+      Map<String, String> actualMap = SaccadeVelocity.analyze(gazeData);
+      assertEquals(1, actualMap.size());
+      assertEquals(EXPECTED_AVG_PEAK, Double.parseDouble(actualMap.get(KEY)), PRECISION);
+
+   }
+}