Fix issue #27

Author: tdebatty

src/main/java/info/debatty/java/stringsimilarity/NGram.java

@@ -46,6 +46,10 @@ public final double distance(final String s0, final String s1) {
         final int sl = s0.length();
         final int tl = s1.length();
 
+        if (s0.equals(s1)) {
+            return 0;
+        }
+
         if (sl == 0 || tl == 0) {
             if (sl == tl) {
                 return 0;

src/test/java/info/debatty/java/stringsimilarity/NGramTest.java

@@ -25,6 +25,7 @@
 package info.debatty.java.stringsimilarity;
 
 import org.junit.Assert;
+import static org.junit.Assert.assertEquals;
 import org.junit.Test;
 
 /**
@@ -46,6 +47,13 @@ public void testDistance() {
         System.out.println(ngram.distance(s0, s1));
         System.out.println(ngram.distance(s0, s2));
         Assert.assertTrue(ngram.distance(s0, s1) < ngram.distance(s0, s2));
+
+
+        assertEquals(0.0, ngram.distance("SIJK", "SIJK"), 0.0);
+        assertEquals(0.0, ngram.distance("S", "S"), 0.0);
+        assertEquals(1.0, ngram.distance("", "S"), 0.0);
+        assertEquals(1.0, ngram.distance("", "SIJK"), 0.0);
+
     }
 
 }

src/test/java/info/debatty/java/stringsimilarity/QGramTest.java

@@ -46,5 +46,14 @@ public final void testDistance() {
         // Total: 2
         double result = instance.distance("ABCD", "ABCE");
         assertEquals(2.0, result, 0.0);
+
+        assertEquals(
+                0.0,
+                instance.distance("S", "S"),
+                0.0);
+
+        assertEquals(0.0,
+                instance.distance("012345", "012345"),
+                0.0);
     }
 }