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diff --git a/spec/inputs/test/in_expression_spec.yue b/spec/inputs/test/in_expression_spec.yue
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+describe "in expression", ->
+        it "should check value in table", ->
+                items = {1, 2, 3, 4, 5}
+                assert.is_true 3 in items
+                assert.is_false 10 in items
+
+        it "should work with strings", ->
+                chars = {"a", "b", "c"}
+                assert.is_true "b" in chars
+                assert.is_false "z" in chars
+
+        it "should check keys in table", ->
+                obj = {x: 1, y: 2, z: 3}
+                assert.is_true "x" in obj
+                assert.is_true "y" in obj
+                assert.is_false "w" in obj
+
+        it "should work with mixed types", ->
+                items = {1, "two", true, nil}
+                assert.is_true 1 in items
+                assert.is_true "two" in items
+                assert.is_true true in items
+                assert.is_false false in items
+
+        it "should handle empty table", ->
+                empty = {}
+                assert.is_false 1 in empty
+                assert.is_false "test" in empty
+
+        it "should work in conditional", ->
+                items = {1, 2, 3}
+                result = if 2 in items
+                        "found"
+                else
+                        "not found"
+                assert.same result, "found"
+
+        it "should support negation", ->
+                items = {1, 2, 3}
+                assert.is_true not (4 in items)
+                assert.is_false not (2 in items)
+
+        it "should work with nested tables", ->
+                nested = {{1, 2}, {3, 4}, {5, 6}}
+                assert.is_true {1, 2} in nested
+                assert.is_false {1, 3} in nested
+
+        it "should handle boolean values", ->
+                bools = {true, false}
+                assert.is_true true in bools
+                assert.is_true false in bools
+
+        it "should work in loop", ->
+                items = {1, 2, 3, 4, 5}
+                count = 0
+                for i = 1, 10
+                        count += 1 if i in items
+                assert.same count, 5
+
+        it "should support table as value", ->
+                key1 = {a: 1}
+                key2 = {b: 2}
+                tb = {[key1]: "first", [key2]: "second"}
+
+                -- Note: this tests table reference equality
+                assert.is_true key1 in tb
+                assert.is_true key2 in tb
+
+        it "should work with function results", ->
+                get_items = -> {1, 2, 3}
+                assert.is_true 2 in get_items!
+                assert.is_false 5 in get_items!
+
+        it "should handle nil in table", ->
+                items = {1, nil, 3}
+                assert.is_true nil in items
+                assert.is_true 1 in items
+
+        it "should work with string keys", ->
+                obj = {name: "test", value: 42}
+                assert.is_true "name" in obj
+                assert.is_true "value" in obj
+                assert.is_false "missing" in obj
+
+        it "should support complex expressions", ->
+                items = {1, 2, 3}
+                result = (2 in items) and "yes" or "no"
+                assert.same result, "yes"
+
+        it "should work in comprehension", ->
+                source = {1, 2, 3, 4, 5}
+                allowed = {2, 4}
+                result = [item for item in *source when item in allowed]
+                assert.same result, {2, 4}