Change how we put test libraries on the class path

- Mark our core test-fixtures jar as part of the "cctest", rather than
   a separate library. I'm fairly sure this was actually using the
   classpath version of CC rather than the legacyClasspath version!

 - Add a new "testMinecraftLibrary" configuration, instead of trying to
   infer it from the classpath. We have to jump through some hoops to
   avoid having multiple versions of a library on the classpath at once,
   but it's not too bad.

I'm working on a patch to bsl which might allow us to kill of
legacyClasspath instead. Please, anything is better than this.

projects/core/build.gradle.kts

@@ -50,13 +50,6 @@ tasks.test {
     systemProperty("cct.test-files", layout.buildDirectory.dir("tmp/testFiles").getAbsolutePath())
 }
 
-tasks.testFixturesJar {
-    manifest {
-        // Ensure the test fixtures jar loads as a mod. Thanks FML >_>.
-        attributes("FMLModType" to "GAMELIBRARY")
-    }
-}
-
 val checkChangelog by tasks.registering(cc.tweaked.gradle.CheckChangelog::class) {
     version.set(modVersion)
     whatsNew.set(file("src/main/resources/data/computercraft/lua/rom/help/whatsnew.md"))

projects/forge/build.gradle.kts

@@ -63,18 +63,15 @@ minecraft {
         fun RunConfig.configureForGameTest() {
             val old = lazyTokens["minecraft_classpath"]
             lazyToken("minecraft_classpath") {
-                // We do some terrible hacks here to basically find all things not already on the runtime classpath
-                // and add them. /Except/ for our source sets, as those need to load inside the Minecraft classpath.
-                val testMod = configurations["testModRuntimeClasspath"].resolve()
-                val implementation = configurations.runtimeClasspath.get().resolve()
-                val new = (testMod - implementation)
-                    .asSequence()
-                    .filter { it.isFile && !it.name.endsWith("-test-fixtures.jar") }
-                    .map { it.absolutePath }
-                    .joinToString(File.pathSeparator)
+                // Add all files in testMinecraftLibrary to the classpath.
+                val allFiles = mutableSetOf<String>()
 
                 val oldVal = old?.get()
-                if (oldVal.isNullOrEmpty()) new else oldVal + File.pathSeparator + new
+                if (!oldVal.isNullOrEmpty()) allFiles.addAll(oldVal.split(File.pathSeparatorChar))
+
+                for (file in configurations["testMinecraftLibrary"].resolve()) allFiles.add(file.absolutePath)
+
+                allFiles.joinToString(File.pathSeparator)
             }
 
             property("cctest.sources", project(":common").file("src/testMod/resources/data/cctest").absolutePath)
@@ -84,6 +81,7 @@ minecraft {
             mods.register("cctest") {
                 source(sourceSets["testMod"])
                 source(sourceSets["testFixtures"])
+                source(project(":core").sourceSets["testFixtures"])
             }
         }
 
@@ -113,6 +111,13 @@ mixin {
 
 configurations {
     minecraftLibrary { extendsFrom(minecraftEmbed.get()) }
+
+    val testMinecraftLibrary by registering {
+        isCanBeResolved = true
+        isCanBeConsumed = false
+        // Prevent ending up with multiple versions of libraries on the classpath.
+        shouldResolveConsistentlyWith(minecraftLibrary.get())
+    }
 }
 
 dependencies {
@@ -161,6 +166,10 @@ dependencies {
     testModImplementation(testFixtures(project(":core")))
     testModImplementation(testFixtures(project(":forge")))
 
+    // Ensure our test fixture dependencies are on the classpath
+    "testMinecraftLibrary"(libs.bundles.kotlin)
+    "testMinecraftLibrary"(libs.bundles.test)
+
     testFixturesImplementation(testFixtures(project(":core")))
 }