add guava throwables example (#8984)

Co-authored-by: Mihai Lepadat <mihai.lepadat@irian.at>

guava/src/test/java/com/baeldung/guava/ThrowablesUnitTest.java

@@ -0,0 +1,44 @@
+package com.baeldung.guava;
+
+import com.google.common.base.Throwables;
+import org.junit.Test;
+
+import java.util.function.Supplier;
+
+public class ThrowablesUnitTest {
+
+    @Test(expected = RuntimeException.class)
+    public void whenThrowable_shouldWrapItInRuntimeException() throws Exception {
+        try {
+            throwThrowable(Throwable::new);
+        } catch (Throwable t) {
+            Throwables.propagateIfPossible(t, Exception.class);
+            throw new RuntimeException(t);
+        }
+    }
+
+    @Test(expected = Error.class)
+    public void whenError_shouldPropagateAsIs() throws Exception {
+        try {
+            throwThrowable(Error::new);
+        } catch (Throwable t) {
+            Throwables.propagateIfPossible(t, Exception.class);
+            throw new RuntimeException(t);
+        }
+    }
+
+    @Test(expected = Exception.class)
+    public void whenException_shouldPropagateAsIs() throws Exception {
+        try {
+            throwThrowable(Exception::new);
+        } catch (Throwable t) {
+            Throwables.propagateIfPossible(t, Exception.class);
+            throw new RuntimeException(t);
+        }
+    }
+
+    private <T extends Throwable> void throwThrowable(Supplier<T> exceptionSupplier) throws Throwable {
+        throw exceptionSupplier.get();
+    }
+
+}