add failing nested step for demonstration (#174)

jgiven-examples/src/test/java/com/tngtech/jgiven/examples/nested/NestedStepsTest.java

@@ -1,5 +1,7 @@
 package com.tngtech.jgiven.examples.nested;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 import org.junit.Test;
 import org.testng.Assert;
 
@@ -23,6 +25,17 @@ public void a_scenario_with_nested_steps() {
 
     }
 
+    @Test
+    public void a_scenario_with_a_failing_nested_step_on_purpose() {
+
+        given().I_fill_out_the_registration_form_with_invalid_values();
+
+        when().I_submit_the_form();
+
+        then().the_password_matches();
+
+    }
+
     static class NestedStage extends Stage<NestedStage> {
 
         @ProvidedScenarioState
@@ -45,6 +58,18 @@ public NestedStage I_fill_out_the_registration_form_with_valid_values() {
                 .and().I_enter_a_repeated_password( "password1234" );
         }
 
+        @NestedSteps
+        public NestedStage I_fill_out_the_registration_form_with_invalid_values() {
+            return I_enter_a_name( "Franky" )
+                .and().I_enter_a_email_address( "franky@acme.com" )
+                .and().something_fails_for_demonstration_purposes();
+        }
+
+        public NestedStage something_fails_for_demonstration_purposes() {
+            assertThat( true ).as( "Fails on purpose" ).isFalse();
+            return self();
+        }
+
         @NestedSteps
         public NestedStage I_enter_a_name( String name ) {
             return I_think_a_name( name )