I have been trying to understand how Surefire plugin internally decides which Testing Framework to use ( TestNG, Jupiter, Junit4 etc. )

Does it use reflection and try to find the presence of each framework in the classpath ?
( Looking at the dependencies, Surefire seems to be coming with junit4 in its transitive dependencies - junit:JUnit:jar:4.12 )

CodePudding user response：

It's possible to pass the provider (test-framework type) explicitly, setting an additional plugin dependency, e.g. for TestNG:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-surefire-plugin</artifactId>
    <version>3.0.0-M5</version>
    <dependencies>
      <dependency>
        <groupId>org.apache.maven.surefire</groupId>
        <artifactId>surefire-testng</artifactId>
        <version>3.0.0-M5</version>
      </dependency>
    </dependencies>
  </plugin>

If nothing specified

Surefire normally automatically selects which test-framework provider to use based on the version of TestNG/JUnit present in your project's classpath.

From this doc:

https://maven.apache.org/surefire/maven-surefire-plugin/examples/providers.html

How Surefire plugin internally decides which Testing Framework to use

Let's look at how it's implemented.

There is ProviderInfo interface with method boolean isApplicable();

ProviderInfo.java

I've found multiple implementations in class AbstractSurefireMojo.java

AbstractSurefireMojo.java

for:

• TestNgProviderInfo
• JUnit3ProviderInfo
• JUnit4ProviderInfo
• JUnitPlatformProviderInfo
• JUnitCoreProviderInfo
• DynamicProviderInfo

And there is also a protected method protected List<ProviderInfo> createProviders( TestClassPath testClasspath ) which reference all this implementations.

protected List<ProviderInfo> createProviders( TestClassPath testClasspath )
        throws MojoExecutionException
    {
        Artifact junitDepArtifact = getJunitDepArtifact();
        return providerDetector.resolve( new DynamicProviderInfo( null ),
            new JUnitPlatformProviderInfo( getJUnit5Artifact(), testClasspath ),
            new TestNgProviderInfo( getTestNgArtifact() ),
            new JUnitCoreProviderInfo( getJunitArtifact(), junitDepArtifact ),
            new JUnit4ProviderInfo( getJunitArtifact(), junitDepArtifact ),
            new JUnit3ProviderInfo() );
    }

and ProviderDetector class invokes isApplicable() per each providerInfo in resolve method.

ProviderDetector.java

And looks like the first applicable is selected:

private Optional<ProviderInfo> autoDetectOneWellKnownProvider( ProviderInfo... wellKnownProviders )
    {
        Optional<ProviderInfo> providerInfo = stream( wellKnownProviders )
            .filter( ProviderInfo::isApplicable )
            .findFirst();

        providerInfo.ifPresent( p -> logger.info( "Using auto detected provider "   p.getProviderName() ) );

        return providerInfo;
    }