1 files changed, 17 insertions, 0 deletions
diff --git a/tests/effects/teffects17.nim b/tests/effects/teffects17.nim
new file mode 100644
index 000000000..5e6b83896
--- /dev/null
+++ b/tests/effects/teffects17.nim
@@ -0,0 +1,17 @@
+discard """
+action: compile
+errormsg: "writeSomething(\"a\") has an illegal effect: WriteIO"
+line: 17
+"""
+
+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(msg: string): void {.tags: [WriteIO].} = echo msg
+
+proc illegalEffectNegation() {.forbids: [WriteIO], tags: [ReadIO, WriteIO].} =
+  echo readSomething()
+  writeSomething("a")