Get test coverage of curve_factory to above 90%

[VikingScientist]

As of 4b98c43aa664faebc00c233c19ef6ad4fc30df4e

The lines that are not covered by the tests are

• [ ] 82
• [ ] 169
• [ ] 363-366
• [ ] 370-374
• [ ] 409
• [ ] 420-422
• [ ] 448
• [ ] 501-564
• [ ] 613-658
• [ ] 676-680