Merging multiple rows into one row in sql

Question

CREATE TABLE #test
(
    PurchaseKey VARCHAR(100),
    ItemKey VARCHAR(100),
    column1 VARCHAR(100),
    column2 VARCHAR(100)
)

INSERT INTO #test (PurchaseKey, ItemKey, column1, column2)
    SELECT '52267434', '106502', NULL, '26405'
    UNION ALL
    SELECT '52267434', '106502', NULL, '26337'
    UNION ALL
    SELECT '52267434', '106502', '26337', NULL
    UNION ALL
    SELECT '52267434', '106502', '26405', NULL

SELECT * FROM #test

Result of 4 rows should become 2 rows where the nulls are replaced with the values below it.