internal/getproviders: Tests for MemoizeSource
internal/getproviders: Tests for MemoizeSource

Due to other pressures at the time this was implemented, it was tested
only indirectly through integration tests in other packages. This now
introduces tests for the two main entry points on MemoizeSource.

pdecat/terraform,VladRassokhin/terraform,pdecat/terraform,hashicorp/terraform,apparentlymart/terraform,heimweh/terraform,pryorda/terraform,rnaveiras/terraform,VladRassokhin/terraform,ewbankkit/terraform,pdecat/terraform,apparentlymart/terraform,ewbankkit/terraform,rnaveiras/terraform,pdecat/terraform,ewbankkit/terraform,pryorda/terraform,tommynsong/terraform,VladRassokhin/terraform,apparentlymart/terraform,hashicorp/terraform,tommynsong/terraform,VladRassokhin/terraform,pryorda/terraform,ewbankkit/terraform,heimweh/terraform,heimweh/terraform,apparentlymart/terraform,heimweh/terraform,heimweh/terraform,tommynsong/terraform,apparentlymart/terraform,hashicorp/terraform,rnaveiras/terraform