Luke 1:34,35
"But Mary said to the angel: “How is this to be, since I am having no intercourse with a man?” In answer the angel said to her: “Holy spirit will come upon you, and power of the Most High will overshadow you. For that reason also what is born will be called holy, God’s Son."
Jehovah God put Jesus into Mary through his holy spirit. Jehovah had to do this so when Jesus was born he would have no sin.
Because when a baby is conceived between two parents, their sin is passed down to their children.
Not a test tube, it was a miracle.