A Theory JUnit test is a subset of the Parameterized JUnit test feature.
It is very similar in respects to driving tests with a set of test data, except with a few differences as explained below.
- The test class is annotated with
@RunWith(Theories.class) - The test does not require a constructor to assign values, which reduces the code length.
-
@DataPointand@DataPointsannotations are used to indicate that a public static variable as a source of test data. -
@DataPointis a single test data value same as@Parameter -
@DataPointsis a set of test data (iterable object) same as@Parameters - The tests are annotated with
@Theory
The following demonstrates the use of all the Theory annotations and explains the results.
import org.junit.experimental.theories.DataPoint;
import org.junit.experimental.theories.DataPoints;
import org.junit.experimental.theories.Theories;
import org.junit.experimental.theories.Theory;
import org.junit.runner.RunWith;
@RunWith(Theories.class)
public class TheoryTest {
@DataPoint
public static String actionMovie = "The Expendables";
@DataPoints
public static String[] movieList = new String[] {
"Star Wars",
"The Great Escape",
"Rambo",
"Terminator 2",
"A Beautiful Mind" };
@DataPoint
public static String comedyMovie = "Zoolander";
@DataPoint
public static int sizeOfMovieList = movieList.length;
@Theory
public void movieTest(String movie) {
System.out.println(movie);
}
@Theory
public void sizeTest(int size) {
System.out.println(String.format(
"Movie List Size = %d%n", size));
}
}
The result of this test outputs the movie titles and size of the movie list.
Movie List Size = 5 The Expendables Zoolander Star Wars The Great Escape Rambo Terminator 2 A Beautiful Mind }
Theories use reflection to decide where the test data is used.
In this case the
String
values were used in the
movieTest
and the
int
value used in the
sizeTest
.
The
@DataPoint
values of
"The Expendables"
and
"Zoolander"
appear first before the
@DataPoints
movie list values even though they appear in different positions in the code.
This can be observed if the following
@DataPoint
is added and the test is re-run.
@DataPoint public static String scifiMovie = "Gravity";
The size of the movie list is 5 instead of 7 as the original movie list is not modified by the tests.
References
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