test(pallet-market): add failure tests and code coverage

[th7nder]

Description

Before:

test result: ok. 20 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 3.73s

Filename                            Regions    Missed Regions     Cover   Functions  Missed Functions  Executed       Lines      Missed Lines     Cover    Branches   Missed Branches     Cover
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
pallets/market/src/lib.rs               440               172    60.91%         108                61    43.52%         637               127    80.06%           0                 0         -
primitives/proofs/src/traits.rs           3                 3     0.00%           3                 3     0.00%           3                 3     0.00%           0                 0         -
primitives/proofs/src/types.rs           14                12    14.29%          12                10    16.67%          18                10    44.44%           0                 0         -
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                                   457               187    59.08%         123                74    39.84%         658               140    78.72%           0                 0         -

After:

test result: ok. 49 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 58.71s

Filename                            Regions    Missed Regions     Cover   Functions  Missed Functions  Executed       Lines      Missed Lines     Cover    Branches   Missed Branches     Cover
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
pallets/market/src/lib.rs               585               157    73.16%         131                64    51.15%         859               103    88.01%           0                 0         -
primitives/proofs/src/traits.rs           3                 3     0.00%           3                 3     0.00%           3                 3     0.00%           0                 0         -
primitives/proofs/src/types.rs           14                12    14.29%          12                10    16.67%          18                10    44.44%           0                 0         -
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                                   602               172    71.43%         146                77    47.26%         880               116    86.82%           0                 0         -
cargo llvm-cov -p pallet-market report --ignore-filename-regex "(mock|test)" --html --output-dir coverage/pallet-market

    Finished report saved to coverage/pallet-market/html
cargo llvm-cov -p pallet-market report --ignore-filename-regex "(mock|test)" --lcov --output-path coverage/pallet-market.lcov.info

    Finished report saved to coverage/pallet-market.lcov.info

Important points for reviewers

The test coverage tool is far from ideal, it takes into the account macros and lots of other stuff which we right now don't care about. It's 'good' enough.
To validate what's missing I used my judgement and VS Code highlighting the lines that are not tested.
While coverage increased from 80% to 86% (tests from 20 to 41) and might not look impressive, we tested a lot of critical paths that could break business logic of our parachain.

DISCLAIMER: It needs to be merged after #100.

Checklist

• Are there important points that reviewers should know?
  • If yes, which ones?
• Make sure that you described what this change does.
• If there are follow-ups, have you created issues for them?
  • If yes, which ones? / List them here
• Have you tested this solution?
• Were there any alternative implementations considered?
• Did you document new (or modified) APIs?

[jmg-duarte]

Great job getting all those tests. Once again, the builder was a nice touch

[cernicc]

Great job! Builder 👍