Class AbstractObjectAssert<SELF extends AbstractObjectAssert<SELF,ACTUAL>,ACTUAL>

java.lang.Object
org.assertj.core.api.AbstractAssert<SELF,ACTUAL>
org.assertj.core.api.AbstractObjectAssert<SELF,ACTUAL>
Type Parameters:
SELF - the "self" type of this assertion class. Please read "Emulating 'self types' using Java Generics to simplify fluent API implementation" for more details.
ACTUAL - the type of the "actual" value.
All Implemented Interfaces:
Assert<SELF,ACTUAL>, Descriptable<SELF>, ExtensionPoints<SELF,ACTUAL>
Direct Known Subclasses:
AbstractAtomicFieldUpdaterAssert, AbstractAtomicReferenceAssert, AbstractComparableAssert, AbstractMapAssert, AbstractThrowableAssert, ObjectAssert

public abstract class AbstractObjectAssert<SELF extends AbstractObjectAssert<SELF,ACTUAL>,ACTUAL> extends AbstractAssert<SELF,ACTUAL>
Base class for all implementations of assertions for Objects.
  • Field Details

    • DOUBLE_COMPARATOR_PRECISION

      private static final double DOUBLE_COMPARATOR_PRECISION
      See Also:
    • FLOAT_COMPARATOR_PRECISION

      private static final float FLOAT_COMPARATOR_PRECISION
      See Also:
    • comparatorByPropertyOrField

      private Map<String,Comparator<?>> comparatorByPropertyOrField
    • comparatorByType

      private TypeComparators comparatorByType
  • Constructor Details

    • AbstractObjectAssert

      public AbstractObjectAssert(ACTUAL actual, Class<?> selfType)
  • Method Details

    • defaultTypeComparators

      public static TypeComparators defaultTypeComparators()
    • as

      public SELF as(Description description)
      Description copied from class: AbstractAssert
      Sets the description of the assertion that is going to be called after.

      You must set it before calling the assertion otherwise it is ignored as the failing assertion breaks the chained call by throwing an AssertionError.

      This overloaded version of "describedAs" offers more flexibility than the one taking a String by allowing users to pass their own implementation of a description. For example, a description that creates its value lazily, only when an assertion failure occurs.

      Specified by:
      as in interface Descriptable<SELF extends AbstractObjectAssert<SELF,ACTUAL>>
      Overrides:
      as in class AbstractAssert<SELF extends AbstractObjectAssert<SELF,ACTUAL>,ACTUAL>
      Parameters:
      description - the new description to set.
      Returns:
      this object.
      See Also:
    • as

      public SELF as(String description, Object... args)
      Description copied from class: AbstractAssert
      Sets the description of the assertion that is going to be called after.

      You must set it before calling the assertion otherwise it is ignored as the failing assertion breaks the chained call by throwing an AssertionError.

      The description follows String.format(String, Object...) syntax.

      Example :

       try {
         // set a bad age to Mr Frodo which is really 33 years old.
         frodo.setAge(50);
         // specify a test description (call as() before the assertion !), it supports String format syntax.
         assertThat(frodo.getAge()).as("check %s's age", frodo.getName()).isEqualTo(33);
       } catch (AssertionError e) {
         assertThat(e).hasMessage("[check Frodo's age] expected:<[33]> but was:<[50]>");
       }
      Specified by:
      as in interface Descriptable<SELF extends AbstractObjectAssert<SELF,ACTUAL>>
      Overrides:
      as in class AbstractAssert<SELF extends AbstractObjectAssert<SELF,ACTUAL>,ACTUAL>
      Parameters:
      description - the new description to set.
      args - optional parameter if description is a format String.
      Returns:
      this object.
      See Also:
    • isEqualToIgnoringNullFields

      public SELF isEqualToIgnoringNullFields(Object other)
      Assert that the actual object is equal to the given one by comparing actual's properties/fields with other's not null properties/fields only (including inherited ones).

      It means that if an actual field is not null and the corresponding field in other is null, this field will be ignored in comparison, but the opposite will make assertion fail (null field in actual, not null in other) as the field is used in the performed comparison and the values differ.

      Note that comparison is not recursive, if one of the field is an Object, it will be compared to the other field using its equals method.

      If an object has a field and a property with the same name, the property value will be used over the field.

      Private fields are used in comparison but this can be disabled using Assertions.setAllowComparingPrivateFields(boolean), if disabled only accessible fields values are compared, accessible fields include directly accessible fields (e.g. public) or fields with an accessible getter.

      The objects to compare can be of different types but the properties/fields used in comparison must exist in both, for example if actual object has a name String field, it is expected other object to also have one.

      Example:

       TolkienCharacter frodo = new TolkienCharacter("Frodo", 33, HOBBIT);
       TolkienCharacter mysteriousHobbit = new TolkienCharacter(null, 33, HOBBIT);
      
       // Null fields in other/expected object are ignored, the mysteriousHobbit has null name thus name is ignored
       assertThat(frodo).isEqualToIgnoringNullFields(mysteriousHobbit); // OK
      
       // ... but this is not reversible !
       assertThat(mysteriousHobbit).isEqualToIgnoringNullFields(frodo); // FAIL
      Parameters:
      other - the object to compare actual to.
      Throws:
      NullPointerException - if the actual or other object is null.
      AssertionError - if the actual and the given object are not lenient equals.
      IntrospectionError - if one of actual's field to compare can't be found in the other object.
    • isEqualToComparingOnlyGivenFields

      public SELF isEqualToComparingOnlyGivenFields(Object other, String... propertiesOrFieldsUsedInComparison)
      Assert that the actual object is equal to the given one using a property/field by property/field comparison on the given properties/fields only (fields can be inherited fields or nested fields). This can be handy if equals implementation of objects to compare does not suit you.

      Note that comparison is not recursive, if one of the field is an Object, it will be compared to the other field using its equals method.

      If an object has a field and a property with the same name, the property value will be used over the field.

      Private fields are used in comparison but this can be disabled using Assertions.setAllowComparingPrivateFields(boolean), if disabled only accessible fields values are compared, accessible fields include directly accessible fields (e.g. public) or fields with an accessible getter.

      The objects to compare can be of different types but the properties/fields used in comparison must exist in both, for example if actual object has a name String field, it is expected the other object to also have one.

      Example:

       TolkienCharacter frodo = new TolkienCharacter("Frodo", 33, HOBBIT);
       TolkienCharacter sam = new TolkienCharacter("Sam", 38, HOBBIT);
      
       // frodo and sam both are hobbits, so they are equals when comparing only race
       assertThat(frodo).isEqualToComparingOnlyGivenFields(sam, "race"); // OK
      
       // they are also equals when comparing only race name (nested field).
       assertThat(frodo).isEqualToComparingOnlyGivenFields(sam, "race.name"); // OK
      
       // ... but not when comparing both name and race
       assertThat(frodo).isEqualToComparingOnlyGivenFields(sam, "name", "race"); // FAIL
      Parameters:
      other - the object to compare actual to.
      propertiesOrFieldsUsedInComparison - properties/fields used in comparison.
      Throws:
      NullPointerException - if the actual or other is null.
      AssertionError - if the actual and the given objects are not equals property/field by property/field on given fields.
      IntrospectionError - if one of actual's property/field to compare can't be found in the other object.
      IntrospectionError - if a property/field does not exist in actual.
    • isEqualToIgnoringGivenFields

      public SELF isEqualToIgnoringGivenFields(Object other, String... propertiesOrFieldsToIgnore)
      Assert that the actual object is equal to the given one by comparing their properties/fields except for the given ones (inherited ones are taken into account). This can be handy if equals implementation of objects to compare does not suit you.

      Note that comparison is not recursive, if one of the property/field is an Object, it will be compared to the other field using its equals method.

      If an object has a field and a property with the same name, the property value will be used over the field.

      Private fields are used in comparison but this can be disabled using Assertions.setAllowComparingPrivateFields(boolean), if disabled only accessible fields values are compared, accessible fields include directly accessible fields (e.g. public) or fields with an accessible getter.

      The objects to compare can be of different types but the properties/fields used in comparison must exist in both, for example if actual object has a name String field, it is expected the other object to also have one.

      Example:

       TolkienCharacter frodo = new TolkienCharacter("Frodo", 33, HOBBIT);
       TolkienCharacter sam = new TolkienCharacter("Sam", 38, HOBBIT);
      
       // frodo and sam are equals when ignoring name and age since the only remaining field is race which they share as HOBBIT.
       assertThat(frodo).isEqualToIgnoringGivenFields(sam, "name", "age"); // OK
      
       // ... but they are not equals if only age is ignored as their names differ.
       assertThat(frodo).isEqualToIgnoringGivenFields(sam, "age"); // FAIL
      Parameters:
      other - the object to compare actual to.
      propertiesOrFieldsToIgnore - ignored properties/fields to ignore in comparison.
      Throws:
      NullPointerException - if the actual or given object is null.
      AssertionError - if the actual and the given objects are not equals property/field by property/field after ignoring given fields.
      IntrospectionError - if one of actual's property/field to compare can't be found in the other object.
    • hasNoNullFieldsOrProperties

      public SELF hasNoNullFieldsOrProperties()
      Assert that the actual object has no null fields or properties (inherited ones are taken into account).

      If an object has a field and a property with the same name, the property value will be used over the field.

      Private fields are checked but this can be disabled using Assertions.setAllowComparingPrivateFields(boolean), if disabled only accessible fields values are checked, accessible fields include directly accessible fields (e.g. public) or fields with an accessible getter.

      Example:

       TolkienCharacter frodo = new TolkienCharacter("Frodo", 33, HOBBIT);
       TolkienCharacter sam = new TolkienCharacter("Sam", 38, null);
      
       // assertion succeeds since all frodo's fields are set
       assertThat(frodo).hasNoNullFields();
      
       // assertion succeeds because sam does not have its race set
       assertThat(sam).hasNoNullFields();
      Throws:
      AssertionError - if the actual object is null.
      AssertionError - if some fields or properties of the actual object are null.
      Since:
      2.5.0 / 3.5.0
    • hasNoNullFieldsOrPropertiesExcept

      public SELF hasNoNullFieldsOrPropertiesExcept(String... propertiesOrFieldsToIgnore)
      Assert that the actual object has no null fields or properties except for the given ones (inherited ones are taken into account).

      If an object has a field and a property with the same name, the property value will be used over the field.

      Private fields are checked but this can be disabled using Assertions.setAllowComparingPrivateFields(boolean), if disabled only accessible fields values are checked, accessible fields include directly accessible fields (e.g. public) or fields with an accessible getter.

      Example:

       TolkienCharacter frodo = new TolkienCharacter("Frodo", 33, null);
      
       // assertion succeeds since frodo has only null field is race
       assertThat(frodo).hasNoNullFieldsExcept("race");
      
       // ... but if we require the race field, the assertion fails
       assertThat(frodo).hasNoNullFieldsExcept("name", "age");
      Parameters:
      propertiesOrFieldsToIgnore - properties/fields that won't be checked for null.
      Throws:
      AssertionError - if the actual object is null.
      AssertionError - if some (non ignored) fields or properties of the actual object are null.
      Since:
      2.5.0 / 3.5.0
    • isEqualToComparingFieldByField

      public SELF isEqualToComparingFieldByField(Object other)
      Assert that actual object is equal to the given object based on a property/field by property/field comparison (including inherited ones). This can be handy if equals implementation of objects to compare does not suit you.

      Note that comparison is not recursive, if one of the field is an Object, it will be compared to the other field using its equals method.

      If an object has a field and a property with the same name, the property value will be used over the field.

      Private fields are used in comparison but this can be disabled using Assertions.setAllowComparingPrivateFields(boolean), if disabled only accessible fields values are compared, accessible fields include directly accessible fields (e.g. public) or fields with an accessible getter.

      The objects to compare can be of different types but the properties/fields used in comparison must exist in both, for example if actual object has a name String field, it is expected the other object to also have one.

      Example:

       // equals not overridden in TolkienCharacter
       TolkienCharacter frodo = new TolkienCharacter("Frodo", 33, HOBBIT);
       TolkienCharacter frodoClone = new TolkienCharacter("Frodo", 33, HOBBIT);
      
       // Fail as equals compares object references
       assertThat(frodo).isEqualsTo(frodoClone);
      
       // frodo and frodoClone are equals when doing a field by field comparison.
       assertThat(frodo).isEqualToComparingFieldByField(frodoClone);
      Parameters:
      other - the object to compare actual to.
      Throws:
      AssertionError - if the actual object is null.
      AssertionError - if the actual and the given objects are not equals property/field by property/field.
      IntrospectionError - if one of actual's property/field to compare can't be found in the other object.
    • usingComparatorForFields

      public <T> SELF usingComparatorForFields(Comparator<T> comparator, String... propertiesOrFields)
      Allows to set a specific comparator to compare properties or fields with the given names. A typical usage is for comparing double/float fields with a given precision.

      Comparators specified by this method have precedence over comparators added by usingComparatorForType(java.util.Comparator<T>, java.lang.Class<T>).

      The comparators specified by this method are only used for field by field comparison like isEqualToComparingFieldByField(Object).

      Example:

       public class TolkienCharacter {
         private String name;
         private double height;
         // constructor omitted
       }
       TolkienCharacter frodo = new TolkienCharacter("Frodo", 1.2);
       TolkienCharacter tallerFrodo = new TolkienCharacter("Frodo", 1.3);
       TolkienCharacter reallyTallFrodo = new TolkienCharacter("Frodo", 1.9);
      
       Comparator<Double> closeEnough = new Comparator<Double>() {
         double precision = 0.5;
         public int compare(Double d1, Double d2) {
           return Math.abs(d1 - d2) invalid input: '<'= precision ? 0 : 1;
         }
       };
      
       // assertions will pass
       assertThat(frodo).usingComparatorForFields(closeEnough, "height")
                        .isEqualToComparingFieldByField(tallerFrodo);
      
       assertThat(frodo).usingComparatorForFields(closeEnough, "height")
                        .isEqualToIgnoringNullFields(tallerFrodo);
      
       assertThat(frodo).usingComparatorForFields(closeEnough, "height")
                        .isEqualToIgnoringGivenFields(tallerFrodo);
      
       assertThat(frodo).usingComparatorForFields(closeEnough, "height")
                        .isEqualToComparingOnlyGivenFields(tallerFrodo);
      
       // assertion will fail
       assertThat(frodo).usingComparatorForFields(closeEnough, "height")
                        .isEqualToComparingFieldByField(reallyTallFrodo);

      Parameters:
      comparator - the Comparator to use
      propertiesOrFields - the names of the properties and/or fields the comparator should be used for
      Returns:
      this assertions object
    • usingComparatorForType

      public <T> SELF usingComparatorForType(Comparator<T> comparator, Class<T> type)
      Allows to set a specific comparator to compare properties or fields with the given type. A typical usage is for comparing fields of numeric type at a given precision.

      Comparators specified by usingComparatorForFields(java.util.Comparator<T>, java.lang.String...) have precedence over comparators specified by this method.

      The comparators specified by this method are only used for field by field comparison like isEqualToComparingFieldByField(Object).

      Example:

       public class TolkienCharacter {
         private String name;
         private double height;
         // constructor omitted
       }
       TolkienCharacter frodo = new TolkienCharacter("Frodo", 1.2);
       TolkienCharacter tallerFrodo = new TolkienCharacter("Frodo", 1.3);
       TolkienCharacter reallyTallFrodo = new TolkienCharacter("Frodo", 1.9);
      
       Comparator<Double> closeEnough = new Comparator<Double>() {
         double precision = 0.5;
         public int compare(Double d1, Double d2) {
           return Math.abs(d1 - d2) invalid input: '<'= precision ? 0 : 1;
         }
       };
      
       // assertions will pass
       assertThat(frodo).usingComparatorForType(closeEnough, Double.class)
                        .isEqualToComparingFieldByField(tallerFrodo);
      
       assertThat(frodo).usingComparatorForType(closeEnough, Double.class)
                        .isEqualToIgnoringNullFields(tallerFrodo);
      
       assertThat(frodo).usingComparatorForType(closeEnough, Double.class)
                        .isEqualToIgnoringGivenFields(tallerFrodo);
      
       assertThat(frodo).usingComparatorForType(closeEnough, Double.class)
                        .isEqualToComparingOnlyGivenFields(tallerFrodo);
      
       // assertion will fail
       assertThat(frodo).usingComparatorForType(closeEnough, Double.class)
                        .isEqualToComparingFieldByField(reallyTallFrodo);

      If multiple compatible comparators have been registered for a given type, the closest in the inheritance chain to the given type is chosen in the following order:
      1. The comparator for the exact given type
      2. The comparator of a superclass of the given type
      3. The comparator of an interface implemented by the given type

      Parameters:
      comparator - the Comparator to use
      type - the Class of the type the comparator should be used for
      Returns:
      this assertions object
    • hasFieldOrProperty

      public SELF hasFieldOrProperty(String name)
      Assert that the actual object has the specified field or property.

      Private fields are matched by default but this can be changed by calling Assertions.setAllowExtractingPrivateFields(false).

      Example:

       public class TolkienCharacter {
      
         private String name;
         private int age;
         // constructor omitted
      
         public String getName() {
           return this.name;
         }
       }
      
       TolkienCharacter frodo = new TolkienCharacter("Frodo", 33);
      
       // assertions will pass :
       assertThat(frodo).hasFieldOrProperty("name")
                        .hasFieldOrProperty("age"); // private field are matched by default
      
       // assertions will fail :
       assertThat(frodo).hasFieldOrProperty("not_exists");
       assertThat(frodo).hasFieldOrProperty(null);
       // disable looking for private fields
       Assertions.setAllowExtractingPrivateFields(false);
       assertThat(frodo).hasFieldOrProperty("age"); 
      Parameters:
      name - the field/property name to check
      Throws:
      AssertionError - if the actual object is null.
      IllegalArgumentException - if name is null.
      AssertionError - if the actual object has not the given field/property
    • hasFieldOrPropertyWithValue

      public SELF hasFieldOrPropertyWithValue(String name, Object value)
      Assert that the actual object has the specified field or property with the given value.

      Private fields are matched by default but this can be changed by calling Assertions.setAllowExtractingPrivateFields(false).

      Example:

       public class TolkienCharacter {
         private String name;
         private int age;
         // constructor omitted
      
         public String getName() {
           return this.name;
         }
       }
      
       TolkienCharacter frodo = new TolkienCharacter("Frodo", 33);
       TolkienCharacter noname = new TolkienCharacter(null, 33);
      
       // assertions will pass :
       assertThat(frodo).hasFieldOrProperty("name", "Frodo");
       assertThat(frodo).hasFieldOrProperty("age", 33);
       assertThat(noname).hasFieldOrProperty("name", null);
      
       // assertions will fail :
       assertThat(frodo).hasFieldOrProperty("name", "not_equals");
       assertThat(frodo).hasFieldOrProperty(null, 33);
       assertThat(frodo).hasFieldOrProperty("age", null);
       assertThat(noname).hasFieldOrProperty("name", "Frodo");
       // disable extracting private fields
       Assertions.setAllowExtractingPrivateFields(false);
       assertThat(frodo).hasFieldOrProperty("age", 33); 
      Parameters:
      name - the field/property name to check
      value - the field/property expected value
      Throws:
      AssertionError - if the actual object is null.
      IllegalArgumentException - if name is null.
      AssertionError - if the actual object has not the given field/property
      AssertionError - if the actual object has the given field/property but not with the expected value
      See Also:
    • extracting

      public AbstractObjectArrayAssert<?,Object> extracting(String... propertiesOrFields)
      Extract the values of given fields/properties from the object under test into an array, this new array becoming the object under test.

      If you extract "id", "name" and "email" fields/properties then the array will contain the id, name and email values of the object under test, you can then perform array assertions on the extracted values.

      Nested fields/properties are supported, specifying "adress.street.number" is equivalent to get the value corresponding to actual.getAdress().getStreet().getNumber()

      Private fields can be extracted unless you call Assertions.setAllowExtractingPrivateFields(false).

      If the object under test is a Map with String keys, extracting will extract values matching the given fields/properties.

      Example:

       // Create frodo, setting its name, age and Race (Race having a name property)
       TolkienCharacter frodo = new TolkienCharacter("Frodo", 33, HOBBIT);
      
       // let's verify Frodo's name, age and race name:
       assertThat(frodo).extracting("name", "age", "race.name")
                        .containsExactly("Frodo", 33, "Hobbit");
      A property with the given name is looked for first, if it doesn't exist then a field with the given name is looked for, if the field is not accessible (i.e. does not exist) an IntrospectionError is thrown.

      Note that the order of extracted property/field values is consistent with the iteration order of the array under test.

      Parameters:
      propertiesOrFields - the properties/fields to extract from the initial object under test
      Returns:
      a new assertion object whose object under test is the array containing the extracted properties/fields values
      Throws:
      IntrospectionError - if one of the given name does not match a field or property
    • extracting

      @SafeVarargs public final AbstractObjectArrayAssert<?,Object> extracting(Function<? super ACTUAL,Object>... extractors)
      Use the given Functions to extract the values from the object under test into an array, this new array becoming the object under test.

      If the given Functions extract the id, name and email values then the array will contain the id, name and email values of the object under test, you can then perform array assertions on the extracted values.

      Example:

       // Create frodo, setting its name, age and Race (Race having a name property)
       TolkienCharacter frodo = new TolkienCharacter("Frodo", 33, HOBBIT);
       
       // let's verify Frodo's name, age and race name:
       assertThat(frodo).extracting(TolkienCharacter::getName, 
                                    character -> character.age, // public field
                                    character -> character.getRace().getName())
                        .containsExactly("Frodo", 33, "Hobbit");

      Note that the order of extracted values is consistent with the iteration order of the array under test.

      Parameters:
      extractors - the extractor functions to extract a value from an element of the Iterable under test.
      Returns:
      a new assertion object whose object under test is the array containing the extracted values
    • isEqualToComparingFieldByFieldRecursively

      public SELF isEqualToComparingFieldByFieldRecursively(Object other)
      Assert that the object under test (actual) is equal to the given object based on recursive a property/field by property/field comparison (including inherited ones). This can be useful if actual's equals implementation does not suit you. The recursive property/field comparison is not applied on fields having a custom equals implementation, i.e. the overridden equals method will be used instead of a field by field comparison.

      The recursive comparison handles cycles. By default floats are compared with a precision of 1.0E-6 and doubles with 1.0E-15.

      You can specify a custom comparator per (nested) fields or type with respectively usingComparatorForFields(Comparator, String...) and usingComparatorForType(Comparator, Class).

      The objects to compare can be of different types but must have the same properties/fields. For example if actual object has a name String field, it is expected the other object to also have one. If an object has a field and a property with the same name, the property value will be used over the field.

      Example:

       public class Person {
         public String name;
         public double height;
         public Home home = new Home();
         public Person bestFriend;
         // constructor with name and height omitted for brevity
       }
      
       public class Home {
         public Address address = new Address();
       }
      
       public static class Address {
         public int number = 1;
       }
      
       Person jack = new Person("Jack", 1.80);
       jack.home.address.number = 123;
      
       Person jackClone = new Person("Jack", 1.80);
       jackClone.home.address.number = 123;
      
       // cycle are handled in comparison
       jack.bestFriend = jackClone;
       jackClone.bestFriend = jack;
      
       // will fail as equals compares object references
       assertThat(jack).isEqualsTo(jackClone);
      
       // jack and jackClone are equals when doing a recursive field by field comparison
       assertThat(jack).isEqualToComparingFieldByFieldRecursively(jackClone);
      
       // any type/field can be compared with a a specific comparator.
       // let's change  jack's height a little bit
       jack.height = 1.81;
      
       // assertion fails because of the height difference
       // (the default precision comparison for double is 1.0E-15)
       assertThat(jack).isEqualToComparingFieldByFieldRecursively(jackClone);
      
       // this succeeds because we allow a 0.5 tolerance on double
       assertThat(jack).usingComparatorForType(new DoubleComparator(0.5), Double.class)
                       .isEqualToComparingFieldByFieldRecursively(jackClone);
      
       // you can set a comparator on specific fields (nested fields are supported)
       assertThat(jack).usingComparatorForFields(new DoubleComparator(0.5), "height")
                       .isEqualToComparingFieldByFieldRecursively(jackClone);
      Parameters:
      other - the object to compare actual to.
      Throws:
      AssertionError - if the actual object is null.
      AssertionError - if the actual and the given objects are not deeply equal property/field by property/field.
      IntrospectionError - if one property/field to compare can not be found.
    • returns

      public <T> SELF returns(T expected, Function<ACTUAL,T> from)
      Verify that the object under test returns the given expected value from the given Function, a typical usage is to pass a method reference to assert object's property.

      Wrapping the given Function with Assertions.from(Function) makes the assertion more readable.

      Example:

       // from is not mandatory but it makes the assertions more readable 
       assertThat(frodo).returns("Frodo", from(TolkienCharacter::getName))
                        .returns("Frodo", TolkienCharacter::getName) // no from :(
                        .returns(HOBBIT, from(TolkienCharacter::getRace));
      Type Parameters:
      T - the expected value type the given method returns.
      Parameters:
      expected - the value the object under test method's call should return.
      from - Function used to acquire the value to test from the object under test. Must not be null
      Returns:
      this assertion object.
      Throws:
      NullPointerException - if given from function is null