testRemaining{0, 0},
		},
	}, {
		maker: makeSparse{makeReg{5, "abcde"}, sparseHoles{{2, 3}}, 8},
		tests: []testFnc{
			testRemaining{8, 5},
			testWrite{"ab\x00\x00\x00cde", 8, nil},
			testWrite{"a", 0, ErrWriteTooLong},
			testRemaining{0, 0},
		},
	}, {
		maker: makeSparse{makeReg{5, "abcde"}, sparseHoles{{2, 3}}, 8},
		tests: []testFnc{

			testRead{0, "", io.EOF},
		},
	}, {
		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{0, 2}, {5, 3}}, 8},
		tests: []testFnc{
			testRemaining{8, 5},
			testRead{3, "ab\x00", nil},
			testRead{10, "\x00\x00cde", io.EOF},
			testRemaining{0, 0},
		},
	}, {
		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{0, 2}, {5, 3}}, 8},
		tests: []testFnc{
			testRemaining{8, 5},

			t.Errorf(`indexBytePortable(%q, '%c') = %v`, tt.a, b, posp)
		}
	}
}

func TestLastIndexByte(t *testing.T) {
	testCases := []BinOpTest{
		{"", "q", -1},
		{"abcdef", "q", -1},
		{"abcdefabcdef", "a", len("abcdef")},      // something in the middle
		{"abcdefabcdef", "f", len("abcdefabcde")}, // last byte
		{"zabcdefabcdef", "z", 0},                 // first byte