Use BuildConfig plugin instead of systemProperty to fix IntelliJ tests

Author: tschuchortdev

build.gradle

@@ -16,6 +16,7 @@ buildscript {
 plugins {
     id 'java'
     id 'org.jetbrains.kotlin.jvm' version "$kotlin_version"
+    id "com.github.gmazzo.buildconfig" version "2.0.1"
 }
 
 apply plugin: 'kotlin'
@@ -40,6 +41,16 @@ idea {
     }
 }
 
+buildConfig {
+    className = "BuildConfig"
+    packageName = "com.tschuchort.compiletesting"
+    sourceSets {
+        test {
+            buildConfigField 'String', 'KOTLIN_VERSION', "\"$kotlin_version\""
+        }
+    }
+}
+
 dependencies {
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
     testImplementation group: 'junit', name: 'junit', version: '4.12'
@@ -75,7 +86,3 @@ compileTestKotlin {
     kotlinOptions.jvmTarget = "1.8"
     kotlinOptions.freeCompilerArgs += ["-Xskip-runtime-version-check"]
 }
-
-test {
-    systemProperty "KOTLIN_VERSION", "$kotlin_version"
-}

src/test/kotlin/com/tschuchort/compiletesting/KotlinCompilationTests.kt

@@ -632,7 +632,7 @@ class KotlinCompilationTests {
 	fun `detects the plugin provided for compilation via pluginClasspaths property`() {
 		val result = defaultCompilerConfig().apply {
 			sources = listOf(SourceFile.kotlin("kSource.kt", "class KSource"))
-			pluginClasspaths = listOf(classpathOf("kotlin-scripting-compiler-${System.getProperty("KOTLIN_VERSION")}"))
+			pluginClasspaths = listOf(classpathOf("kotlin-scripting-compiler-${BuildConfig.KOTLIN_VERSION}"))
 		}.compile()
 
 		assertThat(result.exitCode).isEqualTo(ExitCode.OK)