Add tests and comment

Author: zbynek

user/super/com/google/gwt/emul/java/util/Objects.java

@@ -153,6 +153,7 @@ public static int checkFromToIndex(int fromIndex, int toIndex, int length) {
   }
 
   public static int checkFromIndexSize(int fromIndex, int size, int length) {
+    // in JS fromIndex + size cannot overflow because int is not limited to 32 bits
     if (fromIndex < 0 || size < 0 || fromIndex + size > length) {
       throw new IndexOutOfBoundsException("Range [" + fromIndex + ", " + (fromIndex + size)
           + ") out of bounds for length " + length);

user/test/com/google/gwt/emultest/java/util/ObjectsTest.java

@@ -111,13 +111,16 @@ public void testRequireNonNull() {
 
   public void testRequireNonNullElse() {
     assertEquals("foo", Objects.requireNonNullElse(hideFromCompiler("foo"), "bar"));
+    assertEquals("bar", Objects.requireNonNullElse(hideFromCompiler(null), "bar"));
     assertThrows(NullPointerException.class,
         () -> Objects.requireNonNullElse(hideFromCompiler(null), null));
   }
 
   public void testRequireNonNullElseGet() {
     assertEquals("foo",
         Objects.requireNonNullElseGet(hideFromCompiler("foo"), () -> "bar"));
+    assertEquals("bar",
+        Objects.requireNonNullElseGet(hideFromCompiler(null), () -> "bar"));
     assertThrows(NullPointerException.class,
         () -> Objects.requireNonNullElseGet(hideFromCompiler(null), null));
     assertThrows(NullPointerException.class,
@@ -137,10 +140,13 @@ public void testCheckIndex() {
         () -> Objects.checkIndex(-5, 5));
     assertThrows(IndexOutOfBoundsException.class,
         () -> Objects.checkIndex(10, 5));
+    assertThrows(IndexOutOfBoundsException.class,
+        () -> Objects.checkIndex(5, 5));
   }
 
   public void testCheckFromToIndex() {
     assertEquals(5, Objects.checkFromToIndex(5, 7, 10));
+    assertEquals(0, Objects.checkFromToIndex(0, 10, 10));
     assertThrows(IndexOutOfBoundsException.class,
         () -> Objects.checkFromToIndex(-5, 1, 5));
     assertThrows(IndexOutOfBoundsException.class,
@@ -151,12 +157,15 @@ public void testCheckFromToIndex() {
 
   public void testCheckFromIndexSize() {
     assertEquals(5, Objects.checkFromIndexSize(5, 2, 10));
+    assertEquals(0, Objects.checkFromIndexSize(0, 10, 10));
     assertThrows(IndexOutOfBoundsException.class,
         () -> Objects.checkFromIndexSize(-5, 1, 5));
     assertThrows(IndexOutOfBoundsException.class,
         () -> Objects.checkFromIndexSize(10, 1,  5));
     assertThrows(IndexOutOfBoundsException.class,
         () -> Objects.checkFromIndexSize(1, 10,  5));
+    assertThrows(IndexOutOfBoundsException.class,
+        () -> Objects.checkFromIndexSize(1, -5,  5));
   }
 
   private void assertThrows(Class<? extends Exception> thrownCheck, Runnable toTest) {
@@ -166,6 +175,5 @@ private void assertThrows(Class<? extends Exception> thrownCheck, Runnable toTes
     } catch (Exception ex) {
       assertEquals(ex.getClass(), thrownCheck);
     }
-
   }
 }