diff --git a/engine/util_test.go b/engine/util_test.go
new file mode 100644
index 0000000..0e1a2d9
--- /dev/null
+++ b/engine/util_test.go
@@ -0,0 +1,107 @@
+package engine
+
+import "testing"
+
+func TestParseAndExecSimple(t *testing.T) {
+	type U struct {
+		Expr string
+		R    float64
+	}
+	exprs := []U{
+		{"1+2", 3},
+		{"-1+2", 1},
+		{"-(1+2)", -3},
+		{"-(1+2)*5", -15},
+		{"-(1+2)*5/3", -5},
+		{"1+(-(1+2)*5/3)", -4},
+		{"3^4", 81},
+		{"3^4.5", 81},
+		{"3.5^4.5", 150.0625},
+		{"8%2", 0},
+		{"8%3", 2},
+		{"8%3.5", 2},
+		{"1e2", 100},
+		{"1e-2", 0.01},
+		{"1e-2+1e2", 100.01},
+		{"1e-2+1e2*6/3", 200.01},
+		{"(1e-2+1e2)*6/3", 200.02},
+		{"(88*8)+(1+1+1+1)+(6/1.5)-(99%9*(2^4))", 712},
+		{"1/3*3", 1},
+		{"123_456_789", 123456789},
+		{"123_456_789___", 123456789},
+		{"pi", 3.141592653589793},
+		{"abs(1)", 1},
+		{"abs(-1)", 1},
+		{"ceil(90.2)", 91},
+		{"ceil(90.8)", 91},
+		{"ceil(90.0)", 90},
+		{"floor(90.2)", 90},
+		{"floor(90.8)", 90},
+		{"floor(90.0)", 90},
+		{"sqrt(4)", 2},
+		{"cbrt(27)", 3},
+		{"sqrt(4) + cbrt(27)", 5},
+		{"sqrt(2^2) + cbrt(3^3)", 5},
+		{"127^2+5/2-sqrt(2^2) + cbrt(3^3)", 16132.5},
+		//{"_123_456_789___", 123456789},
+	}
+	for _, e := range exprs {
+		r, _ := ParseAndExec(e.Expr)
+		if r != e.R {
+			t.Error(e, " ParseAndExec:", r)
+		}
+	}
+}
+
+func TestParseAndExecTrigonometric(t *testing.T) {
+	type U struct {
+		Expr       string
+		RadianMode float64
+		AngleMode  float64
+	}
+	exprs := []U{
+		{"sin(pi/2)", 1, 0.027412133592044294},
+		{"csc(pi/2)", 1, 36.48019577324057},
+		{"cos(0)", 1, 1},
+		{"sec(0)", 1, 1},
+		{"tan(pi/4)", 1, 0.013708642534394057},
+		{"cot(pi/4)", 1, 72.94668290394674},
+
+		{"sin(90)", 0.893996663600558, 1},
+		{"csc(90)", 1.1185724071637082, 1},
+		{"cos(0)", 1, 1},
+		{"sec(0)", 1, 1},
+		{"tan(45)", 1.6197751905438615, 1},
+		{"cot(45)", 0.6173696237835551, 1},
+	}
+	for _, e := range exprs {
+		TrigonometricMode = RadianMode
+		r, _ := ParseAndExec(e.Expr)
+		if r != e.RadianMode {
+			t.Error(e, " ParseAndExec RadianMode:", r)
+		}
+		TrigonometricMode = AngleMode
+		r, _ = ParseAndExec(e.Expr)
+		if r != e.AngleMode {
+			t.Error(e, " ParseAndExec AngleMode:", r)
+		}
+	}
+}
+
+func TestParseAndExecError(t *testing.T) {
+	exprs := []string{
+		"(",
+		"((((((",
+		"1#1",
+		"_123_456_789___",
+		"sin()",
+		"sin",
+		"pi(",
+	}
+	for _, e := range exprs {
+		_, err := ParseAndExec(e)
+		if err == nil {
+			t.Error(e, " this is error expr!")
+		}
+	}
+}