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How to test for mandatory exceptions in TestNG?
TestNG provides an option of tracing the exception handling of code. User can test whether a code throws a desired exception or not. Here the expectedExceptions parameter is used along with the @Test annotation. This annotation is very useful in negative/exception testing.
As per TestNG documentation:
“The list of exceptions that a test method is expected to throw. If no exception or a different than one on this list is thrown, this test will be marked a failure.”
In this article, we will see how to implement expectedExceptions in TestNG.
Approach/Algorithm to solve this problem
Step 1: Create MessageUtil.java in src, which is need to be tested and Add an error condition inside the printMessage() method as shown in Program Code.
Step 2: Create a class ExpectedExceptionTest.java in src, it is a test case class and Add an expected exception ArithmeticException to the testPrintMessage() test case. Please follow the program code as written in next section.
Step 3: Now, create and run the testNG.xml or directly testNG class in IDE or compile and run it using command line.
In the output, user can see tests are passed specially testPrintMessage(). This test calls the messageUtil.printMessage(); And prineMessage() function throws Airthmatic exception since it has step to divide 1/0;
If user removes/commented out the code int b=1/a; Output won’t be passed and it will get failed as shown in Output 2.
Example
The following code for common TestNG class − MessageUtil:
src/ MessageUtil.java
public class MessageUtil {
private String message;
//Constructor
//@param message to be printed
public MessageUtil(String message) {
this.message = message;
}
// prints the message
public void printMessage() {
System.out.println(message);
int a =0;
int b = 1/a;
}
// add "Hi!" to the message
public String salutationMessage() {
message = "Hello " + message;
System.out.println(message);
return message;
}
}
The following code for common TestNG class − ExpectedExceptionTest:
src/ ExpectedExceptionTest.java
import org.testng.Assert;
import org.testng.annotations.Test;
public class ExpectedExceptionTest {
String message = "ExpectedException";
MessageUtil messageUtil = new MessageUtil(message);
@Test(expectedExceptions = ArithmeticException.class)
public void testPrintMessage() {
System.out.println("Inside testPrintMessage()");
messageUtil.printMessage();
}
@Test
public void testSalutationMessage() {
System.out.println("Inside testSalutationMessage()");
message = "Hello " + "ExpectedException";
Assert.assertEquals(message,messageUtil.salutationMessage());
}
}
testng.xml
This is a configuration file that is used to organize and run the TestNG test cases.
It is very handy when limited tests are needed to execute rather than full suite.
<?xml version = "1.0" encoding = "UTF-8"?>
<!DOCTYPE suite SYSTEM "http://testng.org/testng-1.0.dtd" >
<suite name = "Suite1" >
<test name = "test1">
<classes>
<class name = "ExpectedExceptionTest"/>
</classes>
</test>
</suite>
Output
Inside testPrintMessage() ExpectedException Inside testSalutationMessage() Hello ExpectedException =============================================== Suite1 Total tests run: 2, Passes: 2, Failures: 0, Skips: 0 ===============================================
If user removes/commented out the code int b=1/a from messageUtil.printMessage() function; Output won’t be passed and it will get failed as shown in Output 2. The reason is @Test − testPrintMessage() expecting Arithmetic Exception to be thrown but it doesn’t throw any exception.
Output
Inside testPrintMessage() ExpectedException org.testng.TestException: Method ExpectedException.testPrintMessage()[pri:0, instance: ExpectedException@327471b5] should have thrown an exception of type class java.lang.ArithmeticException at org.testng.internal.ExpectedExceptionsHolder.noException(ExpectedExceptionsHolder.java:82) at org.testng.internal.TestInvoker.considerExceptions(TestInvoker.java:749) at org.testng.internal.TestInvoker.invokeMethod(TestInvoker.java:634) at org.testng.internal.TestInvoker.invokeTestMethod(TestInvoker.java:173) at org.testng.internal.MethodRunner.runInSequence(MethodRunner.java:46) at org.testng.internal.TestInvoker$MethodInvocationAgent.invoke(TestInvoker.java:824) at org.testng.internal.TestInvoker.invokeTestMethods(TestInvoker.java:146) at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:146) at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:128) at java.util.ArrayList.forEach(ArrayList.java:1259) at org.testng.TestRunner.privateRun(TestRunner.java:794) at org.testng.TestRunner.run(TestRunner.java:596) at org.testng.SuiteRunner.runTest(SuiteRunner.java:377) at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:371) at org.testng.SuiteRunner.privateRun(SuiteRunner.java:332) at org.testng.SuiteRunner.run(SuiteRunner.java:276) at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:53) at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:96) at org.testng.TestNG.runSuitesSequentially(TestNG.java:1212) at org.testng.TestNG.runSuitesLocally(TestNG.java:1134) at org.testng.TestNG.runSuites(TestNG.java:1063) at org.testng.TestNG.run(TestNG.java:1031) at com.intellij.rt.testng.IDEARemoteTestNG.run(IDEARemoteTestNG.java:66) at com.intellij.rt.testng.RemoteTestNGStarter.main(RemoteTestNGStarter.java:109) Inside testSalutationMessage() Hello ExpectedException =============================================== Suite1 Total tests run: 2, Passes: 1, Failures: 1, Skips: 0 ===============================================
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