Refactor ScalaCompilerForUnitTesting.

Refactor ScalaCompilerForUnitTesting by introducing a new method
`extractApiFromSrc` which better describes the intent than
`compileSrc`. The `compileSrc` becomes a private, utility method.

Also, `compileSrc` method changed it's signature so it can take
multiple source code snippets as input. This functionality will
be used in future commits.

compile/interface/src/test/scala/xsbt/ExtractAPISpecification.scala

@@ -17,7 +17,7 @@ class ExtractAPISpecification extends Specification {
 	def stableExistentialNames: Boolean = {
 		def compileAndGetFooMethodApi(src: String): Def = {
 			val compilerForTesting = new ScalaCompilerForUnitTesting
-			val sourceApi = compilerForTesting.compileSrc(src)
+			val sourceApi = compilerForTesting.extractApiFromSrc(src)
 			val FooApi = sourceApi.definitions().find(_.name() == "Foo").get.asInstanceOf[ClassLike]
 			val fooMethodApi = FooApi.structure().declared().find(_.name == "foo").get
 			fooMethodApi.asInstanceOf[Def]

compile/interface/src/test/scala/xsbt/ScalaCompilerForUnitTesting.scala

@@ -23,24 +23,45 @@ class ScalaCompilerForUnitTesting {
 	 * Compiles given source code using Scala compiler and returns API representation
 	 * extracted by ExtractAPI class.
 	 */
-	def compileSrc(src: String): SourceAPI = {
-		import java.io.FileWriter
+	def extractApiFromSrc(src: String): SourceAPI = {
+		val (Seq(tempSrcFile), analysisCallback) = compileSrcs(src)
+		analysisCallback.apis(tempSrcFile)
+	}
+
+	/**
+	 * Compiles given source code snippets written to a temporary files. Each snippet is
+	 * written to a separate temporary file.
+	 *
+	 * The sequence of temporary files corresponding to passed snippets and analysis
+	 * callback is returned as a result.
+	 */
+	private def compileSrcs(srcs: String*): (Seq[File], TestCallback) = {
 		withTemporaryDirectory { temp =>
 			val analysisCallback = new TestCallback
 			val classesDir = new File(temp, "classes")
 			classesDir.mkdir()
 			val compiler = prepareCompiler(classesDir, analysisCallback)
 			val run = new compiler.Run
-			val srcFile = new File(temp, "Test.scala")
-			srcFile.createNewFile()
-			val fw = new FileWriter(srcFile)
-			fw.write(src)
-			fw.close()
-			run.compile(List(srcFile.getAbsolutePath()))
-			analysisCallback.apis(srcFile)
+			val srcFiles = srcs.toSeq.zipWithIndex map { case (src, i) =>
+				val fileName = s"Test_$i.scala"
+				prepareSrcFile(temp, fileName, src)
+			}
+			val srcFilePaths = srcFiles.map(srcFile => srcFile.getAbsolutePath).toList
+			run.compile(srcFilePaths)
+			(srcFiles, analysisCallback)
 		}
 	}
 
+	private def prepareSrcFile(baseDir: File, fileName: String, src: String): File = {
+		import java.io.FileWriter
+		val srcFile = new File(baseDir, fileName)
+		srcFile.createNewFile()
+		val fw = new FileWriter(srcFile)
+		fw.write(src)
+		fw.close()
+		srcFile
+	}
+
 	private def prepareCompiler(outputDir: File, analysisCallback: AnalysisCallback): CachedCompiler0#Compiler = {
 		val args = Array.empty[String]
 		object output extends SingleOutput {