Investment is something about the mutual consent and provided in the partnership deed. The Partners have to decide whether the investment is to be brought by each partner or not and if it is brought in, in which manner - cash or kind. Here, “kind” means any tangible or intangible asset, knowledge, or time invested by the partner. Sometimes, there are also partners who are included just for profit.
Hence, it is not mandatory that both the partners in a partnership have to invest. But, one has to ensure that every such clause is provided in the partnership deed to avoid any discrepancy in future.