Add a convenience method to add the result of a compilation to another compilation.

Author: vRallev

core/src/main/kotlin/com/tschuchort/compiletesting/KotlinCompilation.kt

@@ -681,3 +681,15 @@ class KotlinCompilation : AbstractKotlinCompilation<K2JVMCompilerArguments>() {
 		const val OPTION_KAPT_KOTLIN_GENERATED = "kapt.kotlin.generated"
     }
 }
+
+/**
+ * Adds the output directory of [previousResult] to the classpath of this compilation. This is a convenience for
+ * ```
+ * this.classpaths += previousResult.outputDirectory
+ * ```
+ */
+fun KotlinCompilation.addPreviousResultToClasspath(
+	previousResult: KotlinCompilation.Result
+): KotlinCompilation = apply {
+	classpaths += previousResult.outputDirectory
+}

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

@@ -894,8 +894,8 @@ class KotlinCompilationTests {
 			.apply {
 				sources = listOf(kSource2)
 				inheritClassPath = true
-				classpaths += result.outputDirectory
 			}
+			.addPreviousResultToClasspath(result)
 			.compile()
 			.apply {
 				assertThat(exitCode).isEqualTo(ExitCode.OK)