Add test case for error handling

- closes gh-10

src/test/java/eu/hinsch/spring/propertiesdecrypter/DecryptingPropertiesApplicationListenerTest.java

@@ -0,0 +1,46 @@
+package eu.hinsch.spring.propertiesdecrypter;
+
+import org.jasypt.exceptions.EncryptionOperationNotPossibleException;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
+import org.springframework.core.env.PropertiesPropertySource;
+import org.springframework.core.env.StandardEnvironment;
+
+import java.util.Properties;
+
+import static org.hamcrest.Matchers.isA;
+
+/**
+ * Created by lh on 27/06/15.
+ */
+public class DecryptingPropertiesApplicationListenerTest {
+
+    @Rule
+    public ExpectedException exception = ExpectedException.none();
+
+    private final DecryptingPropertiesApplicationListener listener = new DecryptingPropertiesApplicationListener();
+
+    @Test
+    public void shouldWrapExceptionOnEncryptionError() {
+        // given
+        StandardEnvironment environment = new StandardEnvironment();
+        Properties props = new Properties();
+        props.put("propertyDecryption.password", "NOT-A-PASSWORD");
+        props.put("someProperty", "{encrypted}NOT-ENCRYPTED");
+        environment.getPropertySources().addFirst(new PropertiesPropertySource("test-env", props));
+
+        exception.expect(RuntimeException.class);
+        exception.expectMessage("Unable to decrypt property value '{encrypted}NOT-ENCRYPTED'");
+        exception.expectCause(isA(EncryptionOperationNotPossibleException.class));
+
+        ApplicationEnvironmentPreparedEvent event = new ApplicationEnvironmentPreparedEvent(new SpringApplication(), new String[0], environment);
+
+        // when
+        listener.onApplicationEvent(event);
+
+        // then -> exception
+    }
+}