Add test_logger as feature to logging (#2586)

## Issue Addressed

Fix #2585

## Proposed Changes

Provide a canonical version of test_logger that can be used
throughout lighthouse.

## Additional Info

This allows tests to conditionally emit logging data by adding
test_logger as the default logger. And then when executing
`cargo test --features logging/test_logger` log output
will be visible:

  wink@3900x:~/lighthouse/common/logging/tests/test-feature-test_logger (Add-test_logger-as-feature-to-logging)
  $ cargo test --features logging/test_logger
      Finished test [unoptimized + debuginfo] target(s) in 0.02s
       Running unittests (target/debug/deps/test_logger-e20115db6a5e3714)

  running 1 test
  Sep 10 12:53:45.212 INFO hi, module: test_logger:8
  test tests::test_fn_with_logging ... ok

  test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

     Doc-tests test-logger

  running 0 tests

  test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

Or, in normal scenarios where logging isn't needed, executing
`cargo test` the log output will not be visible:

  wink@3900x:~/lighthouse/common/logging/tests/test-feature-test_logger (Add-test_logger-as-feature-to-logging)
  $ cargo test
      Finished test [unoptimized + debuginfo] target(s) in 0.02s
       Running unittests (target/debug/deps/test_logger-02e02f8d41e8cf8a)

  running 1 test
  test tests::test_fn_with_logging ... ok

  test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

     Doc-tests test-logger

  running 0 tests

  test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

slasher/Cargo.toml

@@ -30,6 +30,5 @@ types = { path = "../consensus/types" }
 maplit = "1.0.2"
 rayon = "1.3.0"
 tempfile = "3.1.0"
+logging = { path = "../common/logging" }
 
-[features]
-test_logger = []

slasher/src/test_utils.rs

@@ -1,5 +1,3 @@
-use slog::Logger;
-use sloggers::Build;
 use std::collections::HashSet;
 use types::{
     AggregateSignature, AttestationData, AttesterSlashing, BeaconBlockHeader, Checkpoint, Epoch,
@@ -8,17 +6,6 @@ use types::{
 
 pub type E = MainnetEthSpec;
 
-pub fn logger() -> Logger {
-    if cfg!(feature = "test_logger") {
-        sloggers::terminal::TerminalLoggerBuilder::new()
-            .level(sloggers::types::Severity::Trace)
-            .build()
-            .unwrap()
-    } else {
-        sloggers::null::NullLoggerBuilder.build().unwrap()
-    }
-}
-
 pub fn indexed_att(
     attesting_indices: impl AsRef<[u64]>,
     source_epoch: u64,

slasher/tests/attester_slashings.rs

@@ -1,8 +1,9 @@
+use logging::test_logger;
 use maplit::hashset;
 use rayon::prelude::*;
 use slasher::{
     config::DEFAULT_CHUNK_SIZE,
-    test_utils::{att_slashing, indexed_att, logger, slashed_validators_from_slashings, E},
+    test_utils::{att_slashing, indexed_att, slashed_validators_from_slashings, E},
     Config, Slasher,
 };
 use std::collections::HashSet;
@@ -171,7 +172,7 @@ fn slasher_test(
 ) {
     let tempdir = tempdir().unwrap();
     let config = Config::new(tempdir.path().into()).for_testing();
-    let slasher = Slasher::open(config, logger()).unwrap();
+    let slasher = Slasher::open(config, test_logger()).unwrap();
     let current_epoch = Epoch::new(current_epoch);
 
     for (i, attestation) in attestations.iter().enumerate() {
@@ -200,7 +201,7 @@ fn parallel_slasher_test(
 ) {
     let tempdir = tempdir().unwrap();
     let config = Config::new(tempdir.path().into()).for_testing();
-    let slasher = Slasher::open(config, logger()).unwrap();
+    let slasher = Slasher::open(config, test_logger()).unwrap();
     let current_epoch = Epoch::new(current_epoch);
 
     attestations

slasher/tests/proposer_slashings.rs

@@ -1,5 +1,6 @@
+use logging::test_logger;
 use slasher::{
-    test_utils::{block as test_block, logger, E},
+    test_utils::{block as test_block, E},
     Config, Slasher,
 };
 use tempfile::tempdir;
@@ -9,7 +10,7 @@ use types::{Epoch, EthSpec};
 fn empty_pruning() {
     let tempdir = tempdir().unwrap();
     let config = Config::new(tempdir.path().into()).for_testing();
-    let slasher = Slasher::<E>::open(config, logger()).unwrap();
+    let slasher = Slasher::<E>::open(config, test_logger()).unwrap();
     slasher.prune_database(Epoch::new(0)).unwrap();
 }
 
@@ -22,7 +23,7 @@ fn block_pruning() {
     config.chunk_size = 2;
     config.history_length = 2;
 
-    let slasher = Slasher::<E>::open(config.clone(), logger()).unwrap();
+    let slasher = Slasher::<E>::open(config.clone(), test_logger()).unwrap();
     let current_epoch = Epoch::from(2 * config.history_length);
 
     // Pruning the empty database should be safe.

slasher/tests/random.rs

@@ -1,8 +1,9 @@
+use logging::test_logger;
 use rand::prelude::*;
 use rand::{rngs::StdRng, thread_rng, Rng, SeedableRng};
 use slasher::{
     test_utils::{
-        block, indexed_att, logger, slashed_validators_from_attestations,
+        block, indexed_att, slashed_validators_from_attestations,
         slashed_validators_from_slashings, E,
     },
     Config, Slasher,
@@ -47,7 +48,7 @@ fn random_test(seed: u64, test_config: TestConfig) {
     config.chunk_size = 1 << chunk_size_exponent;
     config.history_length = 1 << rng.gen_range(chunk_size_exponent, chunk_size_exponent + 3);
 
-    let slasher = Slasher::<E>::open(config.clone(), logger()).unwrap();
+    let slasher = Slasher::<E>::open(config.clone(), test_logger()).unwrap();
 
     let validators = (0..num_validators as u64).collect::<Vec<u64>>();
 

slasher/tests/wrap_around.rs

@@ -1,7 +1,5 @@
-use slasher::{
-    test_utils::{indexed_att, logger},
-    Config, Error, Slasher,
-};
+use logging::test_logger;
+use slasher::{test_utils::indexed_att, Config, Error, Slasher};
 use tempfile::tempdir;
 use types::Epoch;
 
@@ -13,7 +11,7 @@ fn attestation_pruning_empty_wrap_around() {
     config.chunk_size = 16;
     config.history_length = 16;
 
-    let slasher = Slasher::open(config.clone(), logger()).unwrap();
+    let slasher = Slasher::open(config.clone(), test_logger()).unwrap();
 
     let v = vec![0];
     let history_length = config.history_length as u64;
@@ -48,7 +46,7 @@ fn pruning_with_map_full() {
     config.history_length = 1024;
     config.max_db_size_mbs = 1;
 
-    let slasher = Slasher::open(config, logger()).unwrap();
+    let slasher = Slasher::open(config, test_logger()).unwrap();
 
     let v = vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12];