How to test for error condition from invalid input

I'm trying to do a test:

• The test cases are stored in a slice of structs with input and expect.
• The expect can be int or Error.

The goal is to expect an Error if the input will cause an invalid result. I've learnt that it's not recommended to return an error string in Go. How can I expect an error whilst doing unit testing in Go?

Here's the code:

func TestArrIdx(t *testing.T) {
    arr := [5]int{1, 2, 3, 4, 5}
    tests := []struct {
        input  int
        expect int // or an error
    }{
        {len(arr) - 1, 5},
        {1, 2},
        // {-1, t.Error},
    }
    for _, test := range tests {
        testName := fmt.Sprintf("%d", test.input)
        t.Run(testName, func(t *testing.T) {
            got := arr[test.input]
            if got != test.expect {
                t.Errorf("got %v, want %v", got, test.expect)
            } else {
                fmt.Printf("got %v expect %v\n", got, test.expect)
            }
        })
    }
}