Fix test coverage for gradle plugin

Author: Mathias Düsterhöft

restdocs-api-spec-gradle-plugin/build.gradle.kts

@@ -50,8 +50,10 @@ dependencies {
     jacocoRuntime("org.jacoco:org.jacoco.agent:0.8.2:runtime")
 }
 
+// generate gradle properties file with jacoco agent configured
+// see https://discuss.gradle.org/t/testkit-jacoco-coverage/18792
 val createTestKitFiles by tasks.creating {
-    val outputDir = project.file("$buildDir/testkitFiles")
+    val outputDir = project.file("$buildDir/testkit")
 
     inputs.files(jacocoRuntime)
     outputs.dir(outputDir)

restdocs-api-spec-gradle-plugin/src/test/kotlin/com/epages/restdocs/apispec/gradle/RestdocsOpenApiTaskTestBase.kt

@@ -46,6 +46,8 @@ abstract class RestdocsOpenApiTaskTestBase {
             buildFile = resolve("build.gradle").toFile()
             snippetsFolder = resolve("build/generated-snippets").toFile().apply { mkdirs() }
             outputFolder = resolve("build/openapi").toFile()
+
+            initializeGradleProperties()
         }
     }
 
@@ -245,4 +247,10 @@ abstract class RestdocsOpenApiTaskTestBase {
 
     protected fun outputFileContext(): DocumentContext =
         JsonPath.parse(outputFolder.resolve("$outputFileNamePrefix.$format").readText().also { println(it) })
+
+    private fun Path.initializeGradleProperties() {
+        // jacoco agent configuration
+        resolve("gradle.properties").toFile()
+            .writeText(File("build/testkit/testkit-gradle.properties").readText())
+    }
 }