Add test that checks exception handling on background threads

bramble-api/src/test/java/org/briarproject/bramble/test/ThreadExceptionTest.java

@@ -0,0 +1,32 @@
+package org.briarproject.bramble.test;
+
+import org.junit.Test;
+
+import static org.junit.Assert.fail;
+
+public class ThreadExceptionTest extends BrambleTestCase {
+
+	@Test(expected = AssertionError.class)
+	public void testAssertionErrorMakesTestCaseFail() {
+		// This is what BrambleTestCase does, too:
+		fail();
+	}
+
+	@Test(expected = AssertionError.class)
+	public void testExceptionInThreadMakesTestCaseFail() {
+		Thread t = new Thread(() -> {
+			System.out.println("thread before exception");
+			throw new RuntimeException("boom");
+		});
+
+		t.start();
+		try {
+			t.join();
+			System.out.println("joined thread");
+		} catch (InterruptedException e) {
+			e.printStackTrace();
+		}
+	}
+
+
+}