enhancement request: expand test coverage for main mixOmics functions

[evaham1]

Is your feature request related to a problem? Please describe.
Need to increase test coverage

Describe the solution you'd like
At least 50% coverage on all main mixOmics functions (i.e. the ones that build statistical tests like pca, pls, etc)
To see which functions need more coverage: https://app.codecov.io/gh/mixOmicsTeam/mixOmics/tree/master/R

• check_entry
• ica.def.par
• impute.nipals
• ipca
• sipca
• mint.block.pls
• mint.block.spls
• pcasvd
• wrapper.rgcca