fix(android): Start refactoring to add unit tests

android/KMEA/app/src/main/java/com/tavultesoft/kmea/KMManager.java

@@ -308,6 +308,39 @@ public final class KMManager {
     }
   }
 
+  /**
+   * Count the number of surrogate pairs starting from the end of a character sequence
+   * until we reach dn codepoints.
+   * Doing this the hard way because we can't foreach charSequence in reverse.
+   * @param sequence - the character sequence to analyze
+   * @param dn - the number of code points to count up to
+   * @return int
+   */
+  public static int countSurrogatePairs(CharSequence sequence, int dn) {
+    if ((sequence == null) || (sequence.length() == 0) || (dn <= 0)) {
+      return 0;
+    }
+
+    int numPairs = 0, counter = 0;
+    int lastIndex = sequence.length()-1;
+    try {
+      do {
+        if ((lastIndex - counter > 0) && Character.isLowSurrogate(sequence.charAt(lastIndex - counter))) {
+          numPairs++;
+        }
+        counter++;
+      } while (counter < dn && numPairs < dn);
+
+      return numPairs;
+    } catch (Exception e) {
+      Log.e(TAG, "Error in countSurrogatePairs: " + e);
+      if (counter >= dn) {
+        return numPairs;
+      }
+      return 0;
+    }
+  }
+
   /*
   // TODO: Chromium has a bug where deleteSurroundingText deletes an entire grapheme cluster
   // instead of one code-point.
@@ -325,18 +358,8 @@ public final class KMManager {
       return;
     }
 
-    // Count the number of surrogate pairs in this buffer, backwards from the end
-    // until we reach dn codepoints.
-    // Unfortunately, can't foreach charSequence in reverse
-    int numPairs = 0;
-    int counter=0;
     try {
-      do {
-        if ((lastIndex - counter > 0) && Character.isLowSurrogate(charsBackup.charAt(lastIndex - counter))) {
-          numPairs++;
-        }
-        counter++;
-      } while (counter < dn && numPairs < dn);
+      int numPairs = countSurrogatePairs(charsBackup, dn);
 
       // Chop dn+numPairs code points from the end of charsBackup
       // subSequence indices are start(inclusive) to end(exclusive)

android/KMEA/app/src/test/java/com/tavultesoft/kmea/kmmanager/CountSurrogatePairsTest.java

@@ -0,0 +1,69 @@
+package com.tavultesoft.kmea.kmmanager;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+
+import com.tavultesoft.kmea.KMManager;
+
+@RunWith(RobolectricTestRunner.class)
+public class CountSurrogatePairsTest {
+  // Smiley emoji U+1F600 = D800 DC3D
+  private final String SMILEY = "\uD800\uDC3D";
+
+  // Winking emoji U+1F609 = D800 DC3C
+  private final String WINK = "\uD800\uDC3C";
+
+
+  @Test
+  public void test_invalid_input() {
+
+    // Test invalid input doesn't throw exception
+    CharSequence sequence = null;
+    int numPairs = KMManager.countSurrogatePairs(sequence, 1);
+    Assert.assertEquals(0, numPairs);
+
+    sequence = "test";
+    numPairs = KMManager.countSurrogatePairs(sequence, -1);
+    Assert.assertEquals(0, numPairs);
+
+    numPairs = KMManager.countSurrogatePairs(sequence, sequence.length()+5);
+    Assert.assertEquals(0, numPairs);
+  }
+
+  @Test
+  public void test_zero_pair() {
+    CharSequence sequence = "Zero emojis";
+    int numPairs = KMManager.countSurrogatePairs(sequence, sequence.length());
+    Assert.assertEquals(0, numPairs);
+  }
+
+  @Test
+  public void test_one_pair() {
+
+    // Test for scenarios that expect 1 surrogate pair
+    CharSequence sequence = "HaveA" + SMILEY + "Day";
+    int numPairs = KMManager.countSurrogatePairs(sequence, 4);
+    Assert.assertEquals(1, numPairs);
+
+    sequence = "HaveA" + SMILEY + WINK;
+    numPairs = KMManager.countSurrogatePairs(sequence, 1);
+    Assert.assertEquals(1, numPairs);
+
+    numPairs = KMManager.countSurrogatePairs(sequence, 2);
+    Assert.assertEquals(1, numPairs);
+  }
+
+  @Test
+  public void test_two_pairs() {
+
+    // Test for scenarios that expect 2 surrogate pairs
+    CharSequence sequence = "HaveA" + SMILEY + WINK;
+    int numPairs = KMManager.countSurrogatePairs(sequence, 3);
+    Assert.assertEquals(2, numPairs);
+
+    numPairs = KMManager.countSurrogatePairs(sequence, 4);
+    Assert.assertEquals(2, numPairs);
+  }
+}