1 files changed, 19 insertions, 0 deletions
diff --git a/tests/effects/teffects13.nim b/tests/effects/teffects13.nim
new file mode 100644
index 000000000..73082f997
--- /dev/null
+++ b/tests/effects/teffects13.nim
@@ -0,0 +1,19 @@
+discard """
+action: compile
+errormsg: "writeSomething() has an illegal effect: WriteIO"
+line: 19
+"""
+
+type
+  IO = object of RootEffect ## input/output effect
+  ReadIO = object of IO     ## input effect
+  WriteIO = object of IO    ## output effect
+
+proc readSomething(): string {.tags: [ReadIO].} = ""
+proc writeSomething(): void {.tags: [WriteIO].} = echo "..."
+
+proc noWritesPlease() {.forbids: [WriteIO].} =
+  # this is OK:
+  echo readSomething()
+  # the compiler prevents this:
+  writeSomething()