[MNG-8525] Add an integration test with Maven 4 Plugin Sample

[sparsick]

Add an integration test for a Maven 4 plugin sample.

Based on the sample for Maven 3 plugins

Thanks, @gnodet, for resolving some issues.

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[gnodet]

I think we should add unit test and an IT for the plugin.
This way, this would be a good example to point at when starting a new plugin.

A mojo unit test can be written similar to
https://github.com/apache/maven-deploy-plugin/blob/master/src/test/java/org/apache/maven/plugins/deploy/DeployMojoTest.java

I think it would be nice to add a mojo parameter to HelloMojo, maybe pass it to the hello() method. And maybe a skip parameter, that's an easy one to test.

For the IT, we should use the same logic as the outer MavenITmng8525MavenDIPlugin but inside a plugin IT. See https://github.com/apache/maven-deploy-plugin/tree/master/src/it.

We can do it in another PR if you prefer.

[sparsick]

Thanks, @gnodet, for your feedback. I will expand the pull request.

[sparsick]

I'd like to share a few thoughts that I have during writing the tests (if the mailing list is a better place, I can also share them there):

• During testing I miss a possibility where I can inject mocks to the mojo.
• Is it possible to introduce constructor injection? It would be easier to write mojo test with plain JUnit5. I know that I can add a constructor with parameters, but then I also have to a default constructor because of the DI framework. It feels noisy.

This construction

   @Inject
    public HelloMojo(MavenDIComponent component) {
        this.component = component;
    }

results in runtime error:

org.junit.jupiter.api.extension.ParameterResolutionException: Unable to resolve mojo
        at org.apache.maven.api.plugin.testing.MojoExtension.resolveParameter(MojoExtension.java:201)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
Caused by: org.apache.maven.di.impl.DIException: Error while initializing binding BindingToConstructor[@Named("org.apache.maven.plugins:mavendi-maven-plugin:0.0.1-SNAPSHOT:hello") HelloMojoFactory][]
        at org.apache.maven.di.impl.Binding$1.lambda$compile$0(Binding.java:109)
        at org.apache.maven.di.impl.InjectorImpl.getInstance(InjectorImpl.java:75)
        at org.apache.maven.api.di.testing.MavenDIExtension.lookup(MavenDIExtension.java:99)
        at org.apache.maven.api.plugin.testing.MojoExtension.resolveParameter(MojoExtension.java:181)
        ... 2 more
Caused by: org.apache.maven.di.impl.DIException: Failed to call constructor public org.apache.maven.plugins.HelloMojoFactory() to provide requested key @Named("org.apache.maven.plugins:mavendi-maven-plugin:0.0.1-SNAPSHOT:hello") HelloMojoFactory
        at org.apache.maven.di.impl.ReflectionUtils.lambda$bindingFromConstructor$7(ReflectionUtils.java:373)
        at org.apache.maven.di.impl.Binding$BindingToConstructor.lambda$compile$0(Binding.java:188)
        at org.apache.maven.di.impl.Binding$1.lambda$compile$0(Binding.java:105)
        ... 5 more
Caused by: java.lang.NoSuchMethodError: org.apache.maven.plugins.HelloMojo: method 'void <init>()' not found
        at org.apache.maven.plugins.HelloMojoFactory.<init>(HelloMojoFactory.java)
        at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:502)
        at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:486)
        at org.apache.maven.di.impl.ReflectionUtils.lambda$bindingFromConstructor$7(ReflectionUtils.java:360)
        ... 7 more

[gnodet]

I'd like to share a few thoughts that I have during writing the tests (if the mailing list is a better place, I can also share them there):

• During testing I miss a possibility where I can inject mocks to the mojo.
• Is it possible to introduce constructor injection? It would be easier to write mojo test with plain JUnit5. I know that I can add a constructor with parameters, but then I also have to a default constructor because of the DI framework. It feels noisy.

This construction

   @Inject
    public HelloMojo(MavenDIComponent component) {
        this.component = component;
    }

results in runtime error:

org.junit.jupiter.api.extension.ParameterResolutionException: Unable to resolve mojo
        at org.apache.maven.api.plugin.testing.MojoExtension.resolveParameter(MojoExtension.java:201)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
Caused by: org.apache.maven.di.impl.DIException: Error while initializing binding BindingToConstructor[@Named("org.apache.maven.plugins:mavendi-maven-plugin:0.0.1-SNAPSHOT:hello") HelloMojoFactory][]
        at org.apache.maven.di.impl.Binding$1.lambda$compile$0(Binding.java:109)
        at org.apache.maven.di.impl.InjectorImpl.getInstance(InjectorImpl.java:75)
        at org.apache.maven.api.di.testing.MavenDIExtension.lookup(MavenDIExtension.java:99)
        at org.apache.maven.api.plugin.testing.MojoExtension.resolveParameter(MojoExtension.java:181)
        ... 2 more
Caused by: org.apache.maven.di.impl.DIException: Failed to call constructor public org.apache.maven.plugins.HelloMojoFactory() to provide requested key @Named("org.apache.maven.plugins:mavendi-maven-plugin:0.0.1-SNAPSHOT:hello") HelloMojoFactory
        at org.apache.maven.di.impl.ReflectionUtils.lambda$bindingFromConstructor$7(ReflectionUtils.java:373)
        at org.apache.maven.di.impl.Binding$BindingToConstructor.lambda$compile$0(Binding.java:188)
        at org.apache.maven.di.impl.Binding$1.lambda$compile$0(Binding.java:105)
        ... 5 more
Caused by: java.lang.NoSuchMethodError: org.apache.maven.plugins.HelloMojo: method 'void <init>()' not found
        at org.apache.maven.plugins.HelloMojoFactory.<init>(HelloMojoFactory.java)
        at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:502)
        at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:486)
        at org.apache.maven.di.impl.ReflectionUtils.lambda$bindingFromConstructor$7(ReflectionUtils.java:360)
        ... 7 more

It is possible to inject a mock component into the mojo in unit test.
See how it can be done at:
https://github.com/apache/maven-install-plugin/blob/master/src/test/java/org/apache/maven/plugins/install/InstallMojoTest.java#L162-L172
That one will be injected in the mojo under test:
https://github.com/apache/maven-install-plugin/blob/master/src/main/java/org/apache/maven/plugins/install/InstallMojo.java#L55

[sparsick]

Thanks for the link. I will adjust the test to demonstrate it.