# lt.sexrelation failes for wrong input

    First argument is not an object of class mortaar_life_table.

# lt.sexrelation produces the right output

    {
      "type": "list",
      "attributes": {
        "names": {
          "type": "character",
          "attributes": {},
          "value": ["method", "value", "description"]
        },
        "class": {
          "type": "character",
          "attributes": {},
          "value": ["data.frame"]
        },
        "row.names": {
          "type": "integer",
          "attributes": {},
          "value": [1, 2, 3, 4]
        }
      },
      "value": [
        {
          "type": "character",
          "attributes": {},
          "value": ["MI", "Ratio_F_M", "MMR1", "MMR2"]
        },
        {
          "type": "double",
          "attributes": {},
          "value": [0.67, 2.36, 449, 4.49]
        },
        {
          "type": "character",
          "attributes": {},
          "value": ["Masculinity index", "Ratio of females to males aged 20--24", "Maternal mortality per 100,000 births", "Maternal mortality per 1,000 births"]
        }
      ]
    }

# lt.sexrelation failes for wrong second input element

    At least one of the datasets does not seem to be a mortAAR life table.