Fix bux where Strings.join returns empty String (#2465)

CHANGES.txt

@@ -1,4 +1,5 @@
 Current
+Fixed: GITHUB-2465: Fix bux where Strings.join returns empty String
 Fixed: GITHUB-1632: throwing SkipException sets iTestResult status to Failure instead of Skip (Julien Herr & Krishnan Mahadevan)
 New  : GITHUB-2456: Add onDataProviderFailure listener (Krishnan Mahadevan)
 Fixed: GITHUB-2445: NPE in FailedReporter.java With Tests Created in Factory (Arham Jain)

src/main/java/org/testng/util/Strings.java

@@ -67,7 +67,7 @@ public static String join(String delimiter, String[] parts) {
     for (int i = 0; i < parts.length - 1; i++) {
       sb.append(parts[i]).append(delimiter);
     }
-    if (parts.length > 1) {
+    if (parts.length > 0) {
       sb.append(parts[parts.length - 1]);
     }
     return sb.toString();

src/test/java/org/testng/util/StringsTest.java

@@ -0,0 +1,28 @@
+package org.testng.util;
+
+import org.testng.annotations.Test;
+
+import static org.testng.Assert.assertEquals;
+
+/**
+ * Unit tests for {@link Strings}
+ */
+public class StringsTest {
+    @Test
+    public void joinEmptyArray() {
+        String[] emptyArray = new String[0];
+        assertEquals(Strings.join(",", emptyArray), "");
+    }
+
+    @Test
+    public void joinArrayWithOneElement() {
+        String[] array = new String[]{"one"};
+        assertEquals(Strings.join(",", array), "one");
+    }
+
+    @Test
+    public void joinArrayWithTwoElements() {
+        String[] array = new String[]{"one", "two"};
+        assertEquals(Strings.join(",", array), "one,two");
+    }
+}

src/test/resources/testng.xml

@@ -767,6 +767,7 @@
       <class name="org.testng.internal.UtilsTest" />
       <class name="org.testng.internal.ClassHelperTest"/>
       <class name="org.testng.internal.InstanceCreatorTest"/>
+      <class name="org.testng.util.StringsTest"/>
       <class name="test.issue1430.TestFileToClass"/>
     </classes>
   </test>