Verify JaCoCo coverage aggregation yields expected results

In order to detect breakages in the future, a minimum coverage
percentage rule is now being enforced.

gradle/plugins/common/src/main/kotlin/junitbuild.jacoco-aggregation-conventions.gradle.kts

@@ -15,7 +15,24 @@ val classesView = configurations["aggregateCodeCoverageReportResults"].incoming.
 	}
 }
 
-tasks.named<JacocoReport>(jacocoRootReport.reportTask.name).configure {
-	// Override to restore behavior of pre-8.2.1 Gradle (see https://github.com/gradle/gradle/issues/25618)
-	classDirectories.setFrom(classesView.files)
+tasks {
+	val reportTask = named<JacocoReport>(jacocoRootReport.reportTask.name)
+	val jacocoRootCoverageVerification by registering(JacocoCoverageVerification::class) {
+		executionData.from(reportTask.map { it.executionData })
+		classDirectories.from(reportTask.map { it.classDirectories })
+		sourceDirectories.from(reportTask.map { it.sourceDirectories })
+		violationRules {
+			rule {
+				limit {
+					// In order to detect problems with coverage aggregation, we require a minimum coverage percentage
+					minimum = "0.90".toBigDecimal()
+				}
+			}
+		}
+	}
+	reportTask {
+		// Override to restore behavior of pre-8.2.1 Gradle (see https://github.com/gradle/gradle/issues/25618)
+		classDirectories.setFrom(classesView.files)
+		finalizedBy(jacocoRootCoverageVerification)
+	}
 }