Improve detection of NPEs caused by this instance fields being null in Spring unit tests

[IlyaMuravjov]

Description

Fixes #2589 (desired NPE test is generated by fuzzer, because symbolic engine has troubles dealing with getClass() == o.getClass() condition.

To make fuzzer able to generate Object of type Order special JavaLangObjectValueProvider was added that tries to use classUnderTest whenever java.lang.Object is needed (plain new Object() can still be used where java.lang.Object is needed).

In case class under test has some hard to pass validation inside of the constructor and fuzzer is asked to create multiple java.lang.Objects, RemovingConstructFailsUtExecutionInstrumentation was used in all Spring tests (in short, it detects impossible to create due to exceptions thrown by constructor models in stateBefore and replaces them with UtNullModels, making it easier for fuzzer to find "creatable" input and actually call method under test).

Finally, InjectMocksValueProvider was made to respect NonNullSpeculator (previously fuzzer considered all fields to be non-null).

How to test

Manual tests

NPE unit be generated by fuzzer for Order.equals() from spring-boot-testing project.

Generate unit tests for the following classes individually with fuzzer only and with engine only, each of them should generate NPE tests for methods marked with "NPE expected" and no NPE tests for methods marked with "no NPE expected".

package com.rest.order.services; import com.rest.order.models.Order; import com.rest.order.repositories.OrderRepository; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.lang.Nullable; import org.springframework.stereotype.Service; import java.util.List; @Service public class ServiceExample { /// region notAutowired private OrderRepository notAutowired; public void setNotAutowired(OrderRepository notAutowired) { this.notAutowired = notAutowired; } @Autowired public void fakeSetNotAutowired(OrderRepository notAutowired) {} @Autowired public void setNonRequiredNotAutowired(@Autowired(required = false) OrderRepository notAutowired) { this.notAutowired = notAutowired; } @Autowired(required = false) public void nonRequiredSetNotAutowired(OrderRepository notAutowired) { this.notAutowired = notAutowired; } @Autowired public void setNullable(@Nullable OrderRepository notAutowired) { this.notAutowired = notAutowired; } public ServiceExample(OrderRepository notAutowired) { this.notAutowired = notAutowired; } @Autowired(required = false) public ServiceExample(OrderRepository notAutowired, boolean unused) { this.notAutowired = notAutowired; } @Autowired public ServiceExample(@Autowired(required = false) OrderRepository notAutowired, char unused) { this.notAutowired = notAutowired; } // NPE expected public List<Order> useNotAutowired() { return notAutowired.findAll(); } /// endregion /// region autowiredViaConstructor private OrderRepository autowiredViaConstructor; @Autowired public ServiceExample(OrderRepository orderRepository, int unused) { this.autowiredViaConstructor = orderRepository; } // no NPE expected public List<Order> useAutowiredViaConstructor() { return autowiredViaConstructor.findAll(); } /// endregion /// endregion /// region autowiredViaField @Autowired private OrderRepository autowiredViaField; // no NPE expected public List<Order> useAutowiredViaField() { return autowiredViaField.findAll(); } /// endregion /// region autowiredViaSetter private OrderRepository autowiredViaSetter; @Autowired public void setAutowiredViaSetter(OrderRepository orderRepository) { this.autowiredViaSetter = orderRepository; } // no NPE expected public List<Order> useAutowiredViaSetter() { return autowiredViaSetter.findAll(); } /// endregion }

package com.rest.order.services; import com.rest.order.models.Order; import com.rest.order.repositories.OrderRepository; import org.springframework.stereotype.Service; import java.util.List; @Service public class ServiceExample2 { private final OrderRepository autowiredViaOnlyConstructor; public ServiceExample2(OrderRepository orderRepository) { this.autowiredViaOnlyConstructor = orderRepository; } // no NPE expected public List<Order> useAutowiredViaOnlyConstructor() { return autowiredViaOnlyConstructor.findAll(); } }

package com.rest.order.services; import com.rest.order.models.Order; import com.rest.order.repositories.OrderRepository; import java.util.List; public class ServiceExample3 { private final OrderRepository notAutowiredViaOnlyConstructor; public ServiceExample3(OrderRepository orderRepository) { this.notAutowiredViaOnlyConstructor = orderRepository; } // NPE expected public List<Order> useNotAutowiredViaOnlyConstructor() { return notAutowiredViaOnlyConstructor.findAll(); } }

package com.rest.order.services; import com.rest.order.models.Order; import com.rest.order.repositories.OrderRepository; import org.springframework.lang.Nullable; import org.springframework.stereotype.Service; import java.util.List; @Service public class ServiceExample4 { public OrderRepository notAutowiredViaOnlyConstructor; private final OrderService orderService; public ServiceExample4(@Nullable OrderRepository orderRepository, OrderService orderService) { this.notAutowiredViaOnlyConstructor = orderRepository; this.orderService = orderService; } // NPE expected public List<Order> useNotAutowiredViaOnlyConstructor() { return notAutowiredViaOnlyConstructor.findAll(); } }

Self-check list

• I've set the proper labels for my PR (at least, for category and component).
• PR title and description are clear and intelligible.
• I've added enough comments to my code, particularly in hard-to-understand areas.
• The functionality I've repaired, changed or added is covered with automated tests.
• Manual tests have been provided optionally.
• The documentation for the functionality I've been working on is up-to-date.

[IlyaMuravjov]

NOTE: this was not a sufficient condition to guarantee that personOne != personTwo, since engine could have just created one personMock and configure it like this: when(personMock.getName()).thenReturn("k", "123456"), so this test was updated. Discussed changes with original author @tepa46 and added him to reviewers.