Fold classpath test helper into a fixture

Move the inline Greeter.java source out of ScipBuildToolTest's prepare
lambda into a fixture, materialized via copyFixture (now protected).

Author: jupblb

tests/buildTools/src/test/kotlin/tests/BuildToolHarness.kt

@@ -113,10 +113,10 @@ abstract class BuildToolHarness {
      * is non-empty, each token is textually replaced in every file, which lets a
      * single fixture cover parametrized variants (e.g. the JDK in a toolchain).
      */
-    private fun copyFixture(
+    protected fun copyFixture(
         fixture: String,
         target: Path,
-        substitutions: Map<String, String>,
+        substitutions: Map<String, String> = emptyMap(),
     ) {
         val resource = "/fixtures/$fixture"
         val url =

tests/buildTools/src/test/kotlin/tests/ScipBuildToolTest.kt

@@ -37,17 +37,8 @@ class ScipBuildToolTest : BuildToolHarness() {
                 // workspace so its sources are not themselves indexed.
                 prepare = { workingDirectory ->
                     val libSrcDir = Files.createTempDirectory("scip-classpath-lib")
+                    copyFixture("scip/compiles-with-classpath-lib", libSrcDir)
                     val libSrc = libSrcDir.resolve("bar").resolve("Greeter.java")
-                    Files.createDirectories(libSrc.parent)
-                    Files.writeString(
-                        libSrc,
-                        """
-                        |package bar;
-                        |public class Greeter {
-                        |  public String greet() { return "hi"; }
-                        |}
-                        |""".trimMargin(),
-                    )
                     val libClasses = workingDirectory.resolve("lib-classes")
                     Files.createDirectories(libClasses)
                     exec(

tests/buildTools/src/test/resources/fixtures/scip/compiles-with-classpath-lib/bar/Greeter.java

@@ -0,0 +1,4 @@
+package bar;
+public class Greeter {
+  public String greet() { return "hi"; }
+}