Add regression test for #8345

sbt-app/src/sbt-test/tests/fork-main-resources/build.sbt

@@ -0,0 +1,6 @@
+val scalatest = "org.scalatest" %% "scalatest" % "3.2.19"
+
+scalaVersion := "3.7.3"
+Test / fork := true
+libraryDependencies += scalatest % Test
+

sbt-app/src/sbt-test/tests/fork-main-resources/src/main/resources/foo

@@ -0,0 +1,2 @@
+test resource content
+

sbt-app/src/sbt-test/tests/fork-main-resources/src/test/scala/ResourceTest.scala

@@ -0,0 +1,10 @@
+import org.scalatest.funsuite.AnyFunSuite
+
+class ResourceTest extends AnyFunSuite {
+  test("access main resource from forked test") {
+    val loader = Thread.currentThread().getContextClassLoader()
+    val resource = loader.getResource("foo")
+    assert(resource != null, "Resource 'foo' from src/main/resources should be accessible in forked test execution")
+  }
+}
+

sbt-app/src/sbt-test/tests/fork-main-resources/test

@@ -0,0 +1,2 @@
+> test
+