Object.freeze'd mockStockData

[hailey123]

So we don't need to worry about it getting modified by the functions we pass it to and therefore can pull the values we expect out of it to verify results

[coveralls]

Pull Request Test Coverage Report for Build 308

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 64.48%

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Totals
Change from base Build 262:	0.0%
Covered Lines:	291
Relevant Lines:	461

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💛 - Coveralls