JUnit is a popular testing framework in the Java ecosystem that simplifies writing and running tests. The @TestTemplate annotation in JUnit 5 is used to create test templates, which are methods that can be invoked multiple times by different TestTemplateInvocationContext providers. This guide covers the basics of using the @TestTemplate annotation to create test templates in JUnit.
Table of Contents
- Introduction
- Steps to Create a JUnit Test Template
- Real-World Use Case
- Conclusion
Introduction
JUnit provides an easy way to write and execute unit tests for Java applications. The @TestTemplate annotation marks methods that are test templates. These methods are not executed directly but are invoked multiple times by different TestTemplateInvocationContext providers. This is useful for scenarios where the same test logic needs to be executed in different contexts.
Steps to Create a JUnit Test Template
Step 1: Add Maven Dependency
To use JUnit in your project, you need to add the JUnit dependency to your pom.xml file. Use the latest version of JUnit 5:
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<version>5.9.2</version>
<scope>test</scope>
</dependency>
Step 2: Create the Class to be Tested
Create a Java class with methods that you want to test. For example, a simple MathUtils class:
public class MathUtils {
public int add(int a, int b) {
return a + b;
}
public int subtract(int a, int b) {
return a - b;
}
}
Step 3: Create the Test Template Invocation Context Provider
Create a class that implements the TestTemplateInvocationContextProvider interface. This provider will supply the contexts for the test template.
import org.junit.jupiter.api.extension.ExtensionContext;
import org.junit.jupiter.api.extension.TestTemplateInvocationContext;
import org.junit.jupiter.api.extension.TestTemplateInvocationContextProvider;
import java.util.stream.Stream;
public class MathTestTemplateInvocationContextProvider implements TestTemplateInvocationContextProvider {
@Override
public boolean supportsTestTemplate(ExtensionContext context) {
return true;
}
@Override
public Stream<TestTemplateInvocationContext> provideTestTemplateInvocationContexts(ExtensionContext context) {
return Stream.of(
new MathTestTemplateInvocationContext(1, 2, 3),
new MathTestTemplateInvocationContext(2, 3, 5),
new MathTestTemplateInvocationContext(3, 4, 7)
);
}
}
Step 4: Create the Test Template Invocation Context
Create a class that implements the TestTemplateInvocationContext interface. This context will be used for each invocation of the test template.
import org.junit.jupiter.api.extension.ExtensionContext;
import org.junit.jupiter.api.extension.TestTemplateInvocationContext;
import org.junit.jupiter.api.extension.TestTemplateInvocationContextProvider;
import java.util.stream.Stream;
public class MathTestTemplateInvocationContext implements TestTemplateInvocationContext {
private final int a;
private final int b;
private final int expected;
public MathTestTemplateInvocationContext(int a, int b, int expected) {
this.a = a;
this.b = b;
this.expected = expected;
}
public int getA() {
return a;
}
public int getB() {
return b;
}
public int getExpected() {
return expected;
}
}
Step 5: Create the Test Template Class
Create a test class in the src/test/java directory. Use the @TestTemplate annotation to create a test template method. Annotate the test class with @ExtendWith to specify the TestTemplateInvocationContextProvider.
import org.junit.jupiter.api.TestTemplate;
import org.junit.jupiter.api.extension.ExtendWith;
import static org.junit.jupiter.api.Assertions.assertEquals;
@ExtendWith(MathTestTemplateInvocationContextProvider.class)
public class MathUtilsTest {
private final MathUtils mathUtils = new MathUtils();
@TestTemplate
void testAddition(MathTestTemplateInvocationContext context) {
int a = context.getA();
int b = context.getB();
int expected = context.getExpected();
assertEquals(expected, mathUtils.add(a, b), a + " + " + b + " should equal " + expected);
}
}
In this example, the testAddition method is annotated with @TestTemplate and will be executed once for each MathTestTemplateInvocationContext provided by MathTestTemplateInvocationContextProvider. The test logic is the same for each invocation, but the inputs and expected results are different.
Step 6: Run the Test
You can run the test using your IDE, Maven, or Gradle.
Using an IDE:
Most IDEs, like IntelliJ IDEA and Eclipse, have built-in support for running JUnit tests. Simply right-click on your test class or method and select “Run.”
Using Maven:
If you’re using Maven, you can run your tests with the following command:
mvn test
Using Gradle:
If you’re using Gradle, you can run your tests with the following command:
gradle test
Real-World Use Case
In real-world applications, test templates are useful for scenarios where the same test logic needs to be executed in different contexts. For instance, a StringUtils class might need to be tested with different configurations.
Create the Class to be Tested
Create a Java class that contains business logic. For example, a StringUtils class that trims strings:
public class StringUtils {
public String trim(String str) {
return str == null ? null : str.trim();
}
}
In this class, the trim method trims whitespace from a given string.
Create the Test Template Invocation Context Provider
Create a class that implements the TestTemplateInvocationContextProvider interface. This provider will supply the contexts for the test template.
import org.junit.jupiter.api.extension.ExtensionContext;
import org.junit.jupiter.api.extension.TestTemplateInvocationContext;
import org.junit.jupiter.api.extension.TestTemplateInvocationContextProvider;
import java.util.stream.Stream;
public class StringTestTemplateInvocationContextProvider implements TestTemplateInvocationContextProvider {
@Override
public boolean supportsTestTemplate(ExtensionContext context) {
return true;
}
@Override
public Stream<TestTemplateInvocationContext> provideTestTemplateInvocationContexts(ExtensionContext context) {
return Stream.of(
new StringTestTemplateInvocationContext(" hello ", "hello"),
new StringTestTemplateInvocationContext(" world", "world"),
new StringTestTemplateInvocationContext("java ", "java")
);
}
}
Create the Test Template Invocation Context
Create a class that implements the TestTemplateInvocationContext interface. This context will be used for each invocation of the test template.
import org.junit.jupiter.api.extension.ExtensionContext;
import org.junit.jupiter.api.extension.TestTemplateInvocationContext;
public class StringTestTemplateInvocationContext implements TestTemplateInvocationContext {
private final String input;
private final String expected;
public StringTestTemplateInvocationContext(String input, String expected) {
this.input = input;
this.expected = expected;
}
public String getInput() {
return input;
}
public String getExpected() {
return expected;
}
}
Create the Test Template Class
Create a test class for the StringUtils in the src/test/java directory. Use the @TestTemplate annotation to create a test template method. Annotate the test class with @ExtendWith to specify the TestTemplateInvocationContextProvider.
import org.junit.jupiter.api.TestTemplate;
import org.junit.jupiter.api.extension.ExtendWith;
import static org.junit.jupiter.api.Assertions.assertEquals;
@ExtendWith(StringTestTemplateInvocationContextProvider.class)
public class StringUtilsTest {
private final StringUtils stringUtils = new StringUtils();
@TestTemplate
void testTrim(StringTestTemplateInvocationContext context) {
String input = context.getInput();
String expected = context.getExpected();
assertEquals(expected, stringUtils.trim(input), "Trimming '" + input + "' should give '" + expected + "'");
}
}
In this example, the testTrim method is annotated with @TestTemplate and will be executed once for each StringTestTemplateInvocationContext provided by StringTestTemplateInvocationContextProvider. The test logic is the same for each invocation, but the inputs and expected results are different.
Running the Tests
You can run the tests using your IDE, Maven, or Gradle.
Using an IDE:
Most IDEs, like IntelliJ IDEA and Eclipse, have built-in support for running JUnit tests. Simply right-click on your test class or method and select “Run.”
Using Maven:
If you’re using Maven, you can run your tests with the following command:
mvn test
Using Gradle:
If you’re using Gradle, you can run your tests with the following command:
gradle test
Conclusion
The @TestTemplate annotation in JUnit makes it easy to create test templates that can be invoked multiple times by different TestTemplateInvocationContext providers. By using @TestTemplate, you can create flexible and dynamic tests based on various inputs or conditions without writing multiple test cases. Understanding and using the @TestTemplate annotation effectively is crucial
for developing robust and maintainable Java applications.