Add ChecksumInputStreamTest#testAvailable()

Author: garydgregory

src/test/java/org/apache/commons/io/input/ChecksumInputStreamTest.java

@@ -19,6 +19,7 @@
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
@@ -33,6 +34,17 @@
  */
 public class ChecksumInputStreamTest {
 
+    @SuppressWarnings("resource")
+    @Test
+    public void testAvailable() throws Exception {
+        final InputStream shadow;
+        try (InputStream in = ChecksumInputStream.builder().setCharSequence("Hi").get()) {
+            assertTrue(in.available() > 0);
+            shadow = in;
+        }
+        assertEquals(0, shadow.available());
+    }
+
     @Test
     public void testDefaultThresholdFailure() throws IOException {
         final byte[] byteArray = new byte[3];