Make prebuilt_api test environment realistic

Previously, the fixture preparer for prebuilt_apis would add a
core-for-system-modules.jar file in every API directory even though
currently they only exist in the public API directories.

This change makes the test environment more realistic by only creating
them for the public API. Rather than hard code that into the test code
(which would duplicate the hard coding in the decodeSdkDep func) this
extracts a function that is used by both. That ensures that any changes
to that func will be reflected in both the test and runtime behavior.

Bug: 204189791
Test: m nothing
Change-Id: I346ac9c0dcf407c61de16b6027663a05821bcf62
diff --git a/java/testing.go b/java/testing.go
index 0a6a4fa..fafc8d7 100644
--- a/java/testing.go
+++ b/java/testing.go
@@ -159,8 +159,7 @@
 		`, strings.Join(android.SortedStringKeys(release2Modules), `", "`))
 
 	for release, modules := range release2Modules {
-		libs := append([]string{"android", "core-for-system-modules"}, modules...)
-		mockFS.Merge(prebuiltApisFilesForLibs([]string{release}, libs))
+		mockFS.Merge(prebuiltApisFilesForModules([]string{release}, modules))
 	}
 	return android.GroupFixturePreparers(
 		android.FixtureAddTextFile(path, bp),
@@ -168,16 +167,25 @@
 	)
 }
 
-func prebuiltApisFilesForLibs(apiLevels []string, sdkLibs []string) map[string][]byte {
+func prebuiltApisFilesForModules(apiLevels []string, modules []string) map[string][]byte {
+	libs := append([]string{"android"}, modules...)
+
 	fs := make(map[string][]byte)
 	for _, level := range apiLevels {
-		for _, lib := range sdkLibs {
-			for _, scope := range []string{"public", "system", "module-lib", "system-server", "test"} {
-				fs[fmt.Sprintf("prebuilts/sdk/%s/%s/%s.jar", level, scope, lib)] = nil
+		for _, sdkKind := range []android.SdkKind{android.SdkPublic, android.SdkSystem, android.SdkModule, android.SdkSystemServer, android.SdkTest} {
+			// A core-for-system-modules file must only be created for the sdk kind that supports it.
+			if sdkKind == systemModuleKind() {
+				fs[fmt.Sprintf("prebuilts/sdk/%s/%s/core-for-system-modules.jar", level, sdkKind)] = nil
+			}
+
+			for _, lib := range libs {
+				// Create a jar file for every library.
+				fs[fmt.Sprintf("prebuilts/sdk/%s/%s/%s.jar", level, sdkKind, lib)] = nil
+
 				// No finalized API files for "current"
 				if level != "current" {
-					fs[fmt.Sprintf("prebuilts/sdk/%s/%s/api/%s.txt", level, scope, lib)] = nil
-					fs[fmt.Sprintf("prebuilts/sdk/%s/%s/api/%s-removed.txt", level, scope, lib)] = nil
+					fs[fmt.Sprintf("prebuilts/sdk/%s/%s/api/%s.txt", level, sdkKind, lib)] = nil
+					fs[fmt.Sprintf("prebuilts/sdk/%s/%s/api/%s-removed.txt", level, sdkKind, lib)] = nil
 				}
 			}
 		}