Add test cases

[simonsso]

Built on top of #716

Try to make quick improvements of code coverage

[codecov]

Codecov Report

Merging #719 (d577eac) into master (e4ab801) will decrease coverage by 34.39%.
The diff coverage is 7.40%.

❗ Current head d577eac differs from pull request most recent head 52846fb. Consider uploading reports for the commit 52846fb to get more accurate results

@@             Coverage Diff             @@
##           master     #719       +/-   ##
===========================================
- Coverage   77.07%   42.69%   -34.39%     
===========================================
  Files          44       38        -6     
  Lines       11755     4385     -7370     
===========================================
- Hits         9060     1872     -7188     
+ Misses       2695     2513      -182     

Impacted Files	Coverage Δ
pallets/grants/src/lib.rs	76.82% <ø> (+2.93%)	⬆️
pallets/grants/src/weights.rs	0.00% <0.00%> (ø)
pallets/reserve/src/lib.rs	52.94% <ø> (+5.57%)	⬆️
runtimes/eden/src/lib.rs	2.65% <0.00%> (-0.06%)	⬇️
runtimes/eden/src/version.rs	0.00% <ø> (ø)
runtimes/eden/src/weights/frame_system.rs	0.00% <0.00%> (ø)
runtimes/eden/src/weights/mod.rs	0.00% <0.00%> (ø)
runtimes/eden/src/weights/pallet_balances.rs	0.00% <0.00%> (ø)
...imes/eden/src/weights/pallet_collator_selection.rs	0.00% <0.00%> (ø)
runtimes/eden/src/weights/pallet_contracts.rs	0.00% <0.00%> (ø)
... and 14 more

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