BAEL-1801 Add tests for unsigned arithmetic (#4442)

core-java-8/src/test/java/com/baeldung/java8/UnsignedArithmeticUnitTest.java

@@ -0,0 +1,60 @@
+package com.baeldung.java8;
+
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.catchThrowable;
+import static org.junit.Assert.assertEquals;
+
+public class UnsignedArithmeticUnitTest {
+    @Test
+    public void whenDoublingALargeByteNumber_thenOverflow() {
+        byte b1 = 100;
+        byte b2 = (byte) (b1 << 1);
+
+        assertEquals(-56, b2);
+    }
+
+    @Test
+    public void whenComparingNumbers_thenNegativeIsInterpretedAsUnsigned() {
+        int positive = Integer.MAX_VALUE;
+        int negative = Integer.MIN_VALUE;
+
+        int signedComparison = Integer.compare(positive, negative);
+        assertEquals(1, signedComparison);
+
+        int unsignedComparison = Integer.compareUnsigned(positive, negative);
+        assertEquals(-1, unsignedComparison);
+
+        assertEquals(negative, positive + 1);
+    }
+
+    @Test
+    public void whenDividingNumbers_thenNegativeIsInterpretedAsUnsigned() {
+        int positive = Integer.MAX_VALUE;
+        int negative = Integer.MIN_VALUE;
+
+        assertEquals(-1, negative / positive);
+        assertEquals(1, Integer.divideUnsigned(negative, positive));
+
+        assertEquals(-1, negative % positive);
+        assertEquals(1, Integer.divideUnsigned(negative, positive));
+    }
+
+    @Test
+    public void whenParsingNumbers_thenNegativeIsInterpretedAsUnsigned() {
+        Throwable thrown = catchThrowable(() -> Integer.parseInt("2147483648"));
+        assertThat(thrown).isInstanceOf(NumberFormatException.class);
+
+        assertEquals(Integer.MAX_VALUE + 1, Integer.parseUnsignedInt("2147483648"));
+    }
+
+    @Test
+    public void whenFormattingNumbers_thenNegativeIsInterpretedAsUnsigned() {
+        String signedString = Integer.toString(Integer.MIN_VALUE);
+        assertEquals("-2147483648", signedString);
+
+        String unsignedString = Integer.toUnsignedString(Integer.MIN_VALUE);
+        assertEquals("2147483648", unsignedString);
+    }
+}