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POJUnit theory for hashCode/equals contract
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copied!<p>The following class serve as generic tester for equals/hashCode contract. It is a part of a home grown testing framework. </p> <ul> <li>What do you think about?</li> <li>How can I (strong) test this class?</li> <li>It is a good use of Junit theories?</li> </ul> <p>The class: </p> <pre><code>@Ignore @RunWith(Theories.class) public abstract class ObjectTest { // For any non-null reference value x, x.equals(x) should return true @Theory public void equalsIsReflexive(Object x) { assumeThat(x, is(not(equalTo(null)))); assertThat(x.equals(x), is(true)); } // For any non-null reference values x and y, x.equals(y) // should return true if and only if y.equals(x) returns true. @Theory public void equalsIsSymmetric(Object x, Object y) { assumeThat(x, is(not(equalTo(null)))); assumeThat(y, is(not(equalTo(null)))); assumeThat(y.equals(x), is(true)); assertThat(x.equals(y), is(true)); } // For any non-null reference values x, y, and z, if x.equals(y) // returns true and y.equals(z) returns true, then x.equals(z) // should return true. @Theory public void equalsIsTransitive(Object x, Object y, Object z) { assumeThat(x, is(not(equalTo(null)))); assumeThat(y, is(not(equalTo(null)))); assumeThat(z, is(not(equalTo(null)))); assumeThat(x.equals(y) && y.equals(z), is(true)); assertThat(z.equals(x), is(true)); } // For any non-null reference values x and y, multiple invocations // of x.equals(y) consistently return true or consistently return // false, provided no information used in equals comparisons on // the objects is modified. @Theory public void equalsIsConsistent(Object x, Object y) { assumeThat(x, is(not(equalTo(null)))); boolean alwaysTheSame = x.equals(y); for (int i = 0; i < 30; i++) { assertThat(x.equals(y), is(alwaysTheSame)); } } // For any non-null reference value x, x.equals(null) should // return false. @Theory public void equalsReturnFalseOnNull(Object x) { assumeThat(x, is(not(equalTo(null)))); assertThat(x.equals(null), is(false)); } // Whenever it is invoked on the same object more than once // the hashCode() method must consistently return the same // integer. @Theory public void hashCodeIsSelfConsistent(Object x) { assumeThat(x, is(not(equalTo(null)))); int alwaysTheSame = x.hashCode(); for (int i = 0; i < 30; i++) { assertThat(x.hashCode(), is(alwaysTheSame)); } } // If two objects are equal according to the equals(Object) method, // then calling the hashCode method on each of the two objects // must produce the same integer result. @Theory public void hashCodeIsConsistentWithEquals(Object x, Object y) { assumeThat(x, is(not(equalTo(null)))); assumeThat(x.equals(y), is(true)); assertThat(x.hashCode(), is(equalTo(y.hashCode()))); } // Test that x.equals(y) where x and y are the same datapoint // instance works. User must provide datapoints that are not equal. @Theory public void equalsWorks(Object x, Object y) { assumeThat(x, is(not(equalTo(null)))); assumeThat(x == y, is(true)); assertThat(x.equals(y), is(true)); } // Test that x.equals(y) where x and y are the same datapoint instance // works. User must provide datapoints that are not equal. @Theory public void notEqualsWorks(Object x, Object y) { assumeThat(x, is(not(equalTo(null)))); assumeThat(x != y, is(true)); assertThat(x.equals(y), is(false)); } } </code></pre> <p>usage:</p> <pre><code>import org.junit.experimental.theories.DataPoint; public class ObjectTestTest extends ObjectTest { @DataPoint public static String a = "a"; @DataPoint public static String b = "b"; @DataPoint public static String nullString = null; @DataPoint public static String emptyString = ""; } </code></pre>

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