[PowerAssert] Reproduce KT-66208

plugins/power-assert/testData/codegen/operator/NegativeContainsOperator.kt

@@ -1,3 +1,21 @@
 fun box() = expectThrowableMessage {
     assert("Hello" !in listOf("Hello", "World"))
+} + "\n\n" + expectThrowableMessage {
+    // Test that we don't just search for `!in` in the expression.
+    assert(" !in " !in listOf(" !in "))
+} + "\n\n" + expectThrowableMessage {
+    // Test multiline case
+    assert(
+        " !in "
+
+                !in
+
+                listOf(" !in ")
+    )
+} + "\n\n" + expectThrowableMessage {
+    // Test that we don't assume whitespaces around the infix operator
+    assert("Hello"/*!in*/!in/*!in*/listOf("Hello", "World"))
+} + "\n\n" + expectThrowableMessage {
+    // Test nested `!in`
+    assert(("Hello" !in listOf("Hello", "World")) !in listOf(false))
 }