code: def test_pairs(self):
      data = {
          "birthdt": [
              "08jan2009",
              "20dec2008",
              "30dec2008",
              "21dec2008",
              "11jan2009",
          ],
          "birthwt": [1766, 3301, 1454, 3139, 4133],
          "id": [101, 102, 103, 104, 105],
          "sex": ["Male", "Female", "Female", "Female", "Female"],
          "visitdt1": [
              "11jan2009",
              "22dec2008",
              "04jan2009",
              "29dec2008",
              "20jan2009",
          ],
          "visitdt2": [
              "21jan2009",
              np.nan,
              "22jan2009",
              "31dec2008",
              "03feb2009",
          ],
          "visitdt3": [
              "05feb2009",
              np.nan,
              np.nan,
              "02jan2009",
              "15feb2009",
          ],
          "wt1": [1823, 3338, 1549, 3298, 4306],
          "wt2": [2011.0, np.nan, 1892.0, 3338.0, 4575.0],
          "wt3": [2293.0, np.nan, np.nan, 3377.0, 4805.0],
      }
  
      df = DataFrame(data)
  
      spec = {
          "visitdt": [f"visitdt{i:d}" for i in range(1, 4)],
          "wt": [f"wt{i:d}" for i in range(1, 4)],
      }
      result = lreshape(df, spec)
  
      exp_data = {
          "birthdt": [
              "08jan2009",
              "20dec2008",
              "30dec2008",
              "21dec2008",
              "11jan2009",
              "08jan2009",
              "30dec2008",
              "21dec2008",
              "11jan2009",
              "08jan2009",
              "21dec2008",
              "11jan2009",
          ],
          "birthwt": [
              1766,
              3301,
              1454,
              3139,
              4133,
              1766,
              1454,
              3139,
              4133,
              1766,
              3139,
              4133,
          ],
          "id": [
              101,
              102,
              103,
              104,
              105,
              101,
              103,
              104,
              105,
              101,
              104,
              105,
          ],
          "sex": [
              "Male",
              "Female",
              "Female",
              "Female",
              "Female",
              "Male",
              "Female",
              "Female",
              "Female",
              "Male",
              "Female",
              "Female",
          ],
          "visitdt": [
              "11jan2009",
              "22dec2008",
              "04jan2009",
              "29dec2008",
              "20jan2009",
              "21jan2009",
              "22jan2009",
              "31dec2008",
              "03feb2009",
              "05feb2009",
              "02jan2009",
              "15feb2009",
          ],
          "wt": [
              1823.0,
              3338.0,
              1549.0,
              3298.0,
              4306.0,
              2011.0,
              1892.0,
              3338.0,
              4575.0,
              2293.0,
              3377.0,
              4805.0,
          ],
      }
      exp = DataFrame(exp_data, columns=result.columns)
      tm.assert_frame_equal(result, exp)
  
      result = lreshape(df, spec, dropna=False)
      exp_data = {
          "birthdt": [
              "08jan2009",
              "20dec2008",
              "30dec2008",
              "21dec2008",
              "11jan2009",
              "08jan2009",
              "20dec2008",
              "30dec2008",
              "21dec2008",
              "11jan2009",
              "08jan2009",
              "20dec2008",
              "30dec2008",
              "21dec2008",
              "11jan2009",
          ],
          "birthwt": [
              1766,
              3301,
              1454,
              3139,
              4133,
              1766,
              3301,
              1454,
              3139,
              4133,
              1766,
              3301,
              1454,
              3139,
              4133,
          ],
          "id": [
              101,
              102,
              103,
              104,
              105,
              101,
              102,
              103,
              104,
              105,
              101,
              102,
              103,
              104,
              105,
          ],
          "sex": [
              "Male",
              "Female",
              "Female",
              "Female",
              "Female",
              "Male",
              "Female",
              "Female",
              "Female",
              "Female",
              "Male",
              "Female",
              "Female",
              "Female",
              "Female",
          ],
          "visitdt": [
              "11jan2009",
              "22dec2008",
              "04jan2009",
              "29dec2008",
              "20jan2009",
              "21jan2009",
              np.nan,
              "22jan2009",
              "31dec2008",
              "03feb2009",
              "05feb2009",
              np.nan,
              np.nan,
              "02jan2009",
              "15feb2009",
          ],
          "wt": [
              1823.0,
              3338.0,
              1549.0,
              3298.0,
              4306.0,
              2011.0,
              np.nan,
              1892.0,
              3338.0,
              4575.0,
              2293.0,
              np.nan,
              np.nan,
              3377.0,
              4805.0,
          ],
      }
      exp = DataFrame(exp_data, columns=result.columns)
      tm.assert_frame_equal(result, exp)
  
      spec = {
          "visitdt": [f"visitdt{i:d}" for i in range(1, 3)],
          "wt": [f"wt{i:d}" for i in range(1, 4)],
      }
      msg = "All column lists must be same length"
      with pytest.raises(ValueError, match=msg):
          lreshape(df, spec)
  
imports: import re
  import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Index, date_range, lreshape, melt, wide_to_long
  import pandas._testing
label_desc: Use image node_id 1 for calling the TestLreshape obj's underlying member method code with example usage: obj.test_pairs() without return types