Remove dead code warnings from test

[mfornet]

Use workaround proposed here to avoid dead code warning.

[bowenwang1996]

Why do we have dead code in the first place?

[codecov]

Codecov Report

Merging #1963 into staging will increase coverage by 0.09%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           staging    #1963      +/-   ##
===========================================
+ Coverage    86.59%   86.69%   +0.09%     
===========================================
  Files          167      167              
  Lines        31693    31653      -40     
===========================================
- Hits         27444    27440       -4     
+ Misses        4249     4213      -36

Impacted Files	Coverage Δ
chain/network/tests/churn_attack.rs	94.73% <ø> (ø)	⬆️
chain/network/tests/routing.rs	99.52% <ø> (ø)	⬆️
chain/client/src/view_client.rs	69.01% <0%> (-0.93%)	⬇️
chain/jsonrpc/src/lib.rs	75.72% <0%> (-0.37%)	⬇️
chain/jsonrpc/client/src/lib.rs	84.28% <0%> (-0.23%)	⬇️
chain/chain/src/chain.rs	90.53% <0%> (-0.12%)	⬇️
chain/network/tests/cache.rs	93.33% <0%> (-0.09%)	⬇️
chain/jsonrpc/tests/rpc_query.rs	98.07% <0%> (-0.08%)	⬇️
runtime/runtime/src/state_viewer.rs	92.8% <0%> (-0.06%)	⬇️
chain/client/tests/chunks_management.rs	96.17% <0%> (-0.03%)	⬇️
... and 13 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 014793a...28d591c. Read the comment docs.

[mfornet]

Why do we have dead code in the first place?

tl;dr: We don't have dead code, but there is a "bug" in cargo.

It is a "bug" in cargo (or bad design).
My use case was the following, I need to make some common tools for test, but didn't want to put them on src/test_utils.rs since it would make network depend on client (which is undesirable).
But adding it as dev-dependency is ok.

From rust book I found this pattern which was exactly what I needed. The problem with this is that every test file (under the tests folder) is seen by cargo as an independent crate, and since some tests don't use this common tools cargo complain about some dead code.

Read more about this issue on rust-lang/rust#46379 (I also found the fix there).