func TestExprWithEnv(t *testing.T) {
	var cases = []struct {
		expr string
		val  interface{}
	}{
		// env: a = 10, b = "string value",
		{expr: "a", val: 10.0},
		{expr: "b", val: "string value"},
		{expr: "a>10", val: false},
		{expr: "a<11", val: true},
		{expr: "a+1", val: 11.0},
		{expr: "a==10", val: true},
	}

	for _, c := range cases {
		t.Log(c.expr)
		vm, err := parseExpr(c.expr)
		if err != nil {
			t.Fatal(err)
		}
		val := vm.runWithEnv("", nil, map[string]interface{}{"a": 10, "b": "string value"})
		if !reflect.DeepEqual(val, c.val) {
			if f, ok := c.val.(float64); ok && math.IsNaN(f) && math.IsNaN(val.(float64)) {
				continue
			}
			t.Fatalf("expr: %q, got: %v, expect: %v", c.expr, val, c.val)
		}
	}
}