API Standardization through testing

[Affie]

• Restructuring interface test
• Improving test coverage with functions, errors, warnings, deprecation, etc
• Fixing small stuff along the way
• Towards standard API
• Towards test reuse and cross driver tests

ref #134
ref #145
ref #182

Based on #134, default will be an exception (preferably not ErrorException TODO). Then a flag can be added later if we still want.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (develop@b61fd3a). Click here to learn what that means.
The diff coverage is 91.22%.

@@            Coverage Diff             @@
##             develop     #276   +/-   ##
==========================================
  Coverage           ?   68.81%           
==========================================
  Files              ?       42           
  Lines              ?     1783           
  Branches           ?        0           
==========================================
  Hits               ?     1227           
  Misses             ?      556           
  Partials           ?        0

Impacted Files	Coverage Δ
src/entities/DFGVariable/VariableNodeData.jl	75% <ø> (ø)
src/LightDFG/services/LightDFG.jl	95.13% <ø> (ø)
src/sandbox.jl	0% <0%> (ø)
src/GraphsDFG/services/GraphsDFG.jl	94.11% <100%> (ø)
src/CloudGraphsDFG/services/CloudGraphsDFG.jl	74.32% <100%> (ø)
src/services/AbstractDFG.jl	86.41% <100%> (ø)
src/services/DFGFactor.jl	66.66% <100%> (ø)
src/GraphsDFG/entities/GraphsDFG.jl	100% <100%> (ø)
src/services/DFGVariable.jl	74.38% <33.33%> (ø)
src/Deprecated.jl	86.66% <90.47%> (ø)

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