java - How to inject parameter into constructor of TestNG class?

Question

I have implemented a programm with the strategy pattern. So I have an interface which is used at some places and the concrete implementation may be replaced.

Now I want to test this programm. I would like to do it in a similar way. Write a test once, which tests against the interface. The concrete interface implementation should be injected at the beginning of the test, so that I may replace it easily.

My testclass looks similar to this one:

public class MyTestClass {

    private StrategeyInterface strategy;

    public MyTestClass(StrategeyInterface strategy) {
        this.strategy = strategy;
    }
    ....test methods using the strategy.
}

The parameterized contructor must used to be inject the concrete strategy implementation at thr beginning og the tests.

Now I did not get TestNG to run it and inject the concrete implementation instance. I tried several ways with inheritance, @DataProvider, @Factory and the corresponding methods, but without luck.

Here is what the testNG report says:

Can't invoke public void MyClass.myTestMethod(): either make it static or add a no-args constructor to your class

I use the maven surefire plugin to run the tests. Here is the relevant part of the pom.xml:

    <build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-surefire-plugin</artifactId>
            <configuration>
                <suiteXmlFiles>
                    <suiteXmlFile>src/test/resources/testng.xml</suiteXmlFile>
                </suiteXmlFiles>
            </configuration>
        </plugin>
    </plugins>
</build>

How do I write and run the tests, with injecting a concrete implementation into the test class?

Thanks in advance.

P.S. I could deliver more code I tried. I did not post it here, yet, because I tried so many variants so that I am kind of confused now and all of them fail.

Answer 1

You have several options. If you are using Guice, here is a very straightforward way to inject your implementation.

If not, you can use a mix of factories and data provider:

@Factory(dataProvider = "dp")
public FactoryDataProviderSampleTest(StrategyInterface si) {
}

@DataProvider
static public Object[][] dp() {
  return new Object[][] {
    new Object[] { new Strategy1Impl() },
    new Object[] { new Strategy2Impl() },
  };
}