How Does surefire decide on the Test framework? - maven

Question

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 )

Answer 1

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;
}