diff --git a/ucl/testbuiltins_test.go b/ucl/testbuiltins_test.go
index 8094824..7d0ae1c 100644
--- a/ucl/testbuiltins_test.go
+++ b/ucl/testbuiltins_test.go
@@ -1198,3 +1198,35 @@ func TestBuiltins_AndOrNot(t *testing.T) {
 		})
 	}
 }
+
+func TestBuiltins_Cat(t *testing.T) {
+	tests := []struct {
+		desc string
+		expr string
+		want any
+	}{
+		{desc: "cat 1", expr: `cat "hello, " "world"`, want: "hello, world"},
+		{desc: "cat 2", expr: `cat "hello, " "world " "and stuff"`, want: "hello, world and stuff"},
+		{desc: "cat 3", expr: `cat "int = " 123`, want: "int = 123"},
+		{desc: "cat 4", expr: `cat "bool = " $true`, want: "bool = true"},
+		{desc: "cat 5", expr: `cat "array = " []`, want: "array = []"},
+		{desc: "cat 6", expr: `cat "array = " [1 3 2 4]`, want: "array = [1 3 2 4]"},
+		{desc: "cat 7", expr: `cat 1 $true 3 [4]`, want: "1true3[4]"},
+		{desc: "cat 8", expr: `cat`, want: ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ctx := context.Background()
+			outW := bytes.NewBuffer(nil)
+
+			inst := New(WithOut(outW), WithTestBuiltin())
+			inst.SetVar("true", true)
+			inst.SetVar("false", false)
+
+			eqRes, err := inst.Eval(ctx, tt.expr)
+			assert.NoError(t, err)
+			assert.Equal(t, tt.want, eqRes)
+		})
+	}
+}