Revert "Revert "Prevent multiple PackagingSpecs having same inst..."

Revert submission 3069323-revert-3066748-duplicate_entry_fs-CIBDJQYRHU

Reason for revert: relanding with forward fix

Reverted changes: /q/submissionid:3069323-revert-3066748-duplicate_entry_fs-CIBDJQYRHU

Change-Id: Ica5a126446ca2dc07a40e4ff9866389b5d164eab
diff --git a/filesystem/filesystem_test.go b/filesystem/filesystem_test.go
index 1215048..acd4813 100644
--- a/filesystem/filesystem_test.go
+++ b/filesystem/filesystem_test.go
@@ -442,3 +442,26 @@
 		}
 	`)
 }
+
+func TestPreventDuplicatedEntries(t *testing.T) {
+	fixture.ExtendWithErrorHandler(android.FixtureExpectsOneErrorPattern(
+		"packaging conflict at")).
+		RunTestWithBp(t, `
+		android_filesystem {
+			name: "fs",
+			deps: [
+				"foo",
+				"foo_dup",
+			],
+		}
+
+		cc_binary {
+			name: "foo",
+		}
+
+		cc_binary {
+			name: "foo_dup",
+			stem: "foo",
+		}
+	`)
+}