Add cron expression validation function and tests

internal/validate/cron_expression.go

@@ -0,0 +1,22 @@
+package validate
+
+import (
+	"strings"
+
+	"github.com/adhocore/gronx"
+)
+
+// CronExpression validates a cron expression.
+//
+// It only supports 5 fields (minute, hour, day of month, month, day of week).
+//
+// It returns a boolean indicating whether the expression is valid or not.
+func CronExpression(expression string) bool {
+	fields := strings.Fields(expression)
+	if len(fields) != 5 {
+		return false
+	}
+
+	gron := gronx.New()
+	return gron.IsValid(expression)
+}

internal/validate/cron_expression_test.go

@@ -0,0 +1,58 @@
+package validate
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCronExpression(t *testing.T) {
+	tests := []struct {
+		name       string
+		expression string
+		want       bool
+	}{
+		{
+			name:       "Valid 5-field expression",
+			expression: "0 12 * * 1-5",
+			want:       true,
+		},
+		{
+			name:       "Invalid: too few fields",
+			expression: "0 12 * *",
+			want:       false,
+		},
+		{
+			name:       "Invalid: too many fields",
+			expression: "0 12 * * 1-5 2023",
+			want:       false,
+		},
+		{
+			name:       "Invalid: incorrect minute",
+			expression: "60 12 * * 1-5",
+			want:       false,
+		},
+		{
+			name:       "Valid: complex expression",
+			expression: "*/15 2,8-17 * * 1-5",
+			want:       true,
+		},
+		{
+			name:       "Invalid: incorrect day of week",
+			expression: "0 12 * * 8",
+			want:       false,
+		},
+		{
+			name:       "Valid: using names",
+			expression: "0 12 * JAN-DEC MON-FRI",
+			want:       true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := CronExpression(tt.expression)
+			assert.Equal(t, tt.want, got, "CronExpression(%v)", tt.expression)
+		})
+	}
+}