Do not run DeGraph as part of standard test task

Prior to this commit, the slow DeGraph dependency tests were always
executed via the standard Gradle `test` task. The only way to execute
all tests without DeGraph was to execute `gradlew test -x :test` which
is not very intuitive for most developers.

This commit addresses this issue by introducing a new (empty) `degraph`
task in the root project which acts as an "alias" for the
`junitPlatformTest` task.

In addition, the dependency from the standard `test` task to the
`junitPlatformTest` task has been removed for the root project, and a
dependency from the `check` task to the `degraph` task has been added
for the root project.

Consequently, executing `gradlew test` will no longer run the DeGraph
tests, but executing `gradlew degraph` or `gradlew check` will.

Issue: #481

build.gradle

@@ -418,6 +418,26 @@ configure(rootProject) {
 		logManager 'org.apache.logging.log4j.jul.LogManager'
 	}
 
+	task degraph() {
+		description = 'Runs DeGraph tests.'
+		// configured in afterEvaluate
+	}
+
+	afterEvaluate {
+		// The following is a hack which allows the custom `degraph`
+		// task to serve as an "alias" for the `junitPlatformTest` task.
+		// In addition, the following removes the dependency from the
+		// `test` task to the `junitPlatformTest` task (which is
+		// created by the JUnit Platform Gradle Plugin) and adds a
+		// dependency from `check` to `degraph`. Consequently,
+		// executing `gradle test` will not run the DeGraph tests, but
+		// `gradle degraph` or `gradle check` will.
+		def junitPlatformTestTask = tasks.getByName('junitPlatformTest')
+		degraph.dependsOn(junitPlatformTestTask)
+		test.dependsOn.remove(junitPlatformTestTask)
+		check.dependsOn(degraph)
+	}
+
 	task aggregateJavadocs(type: Javadoc) {
 		group = "Documentation"
 		description = "Generates aggregated Javadocs"