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

beacon_node/beacon_chain/Cargo.toml

@@ -8,7 +8,6 @@ edition = "2018"
 default = ["participation_metrics"]
 write_ssz_files = []  # Writes debugging .ssz files to /tmp during block processing.
 participation_metrics = []  # Exposes validator participation metrics to Prometheus.
-test_logger = [] # Print log output to stderr when running tests instead of dropping it
 fork_from_env = [] # Initialise the harness chain spec from the FORK_NAME env variable
 
 [dev-dependencies]
@@ -55,3 +54,4 @@ itertools = "0.10.0"
 slasher = { path = "../../slasher" }
 eth2 = { path = "../../common/eth2" }
 strum = { version = "0.21.0", features = ["derive"] }
+logging = { path = "../../common/logging" }

beacon_node/beacon_chain/src/test_utils.rs

@@ -14,13 +14,13 @@ use bls::get_withdrawal_credentials;
 use futures::channel::mpsc::Receiver;
 pub use genesis::interop_genesis_state;
 use int_to_bytes::int_to_bytes32;
+use logging::test_logger;
 use merkle_proof::MerkleTree;
 use parking_lot::Mutex;
 use rand::rngs::StdRng;
 use rand::Rng;
 use rand::SeedableRng;
 use rayon::prelude::*;
-use slog::Logger;
 use slot_clock::TestingSlotClock;
 use state_processing::state_advance::complete_state_advance;
 use std::borrow::Cow;
@@ -107,25 +107,6 @@ fn make_rng() -> Mutex<StdRng> {
     Mutex::new(StdRng::seed_from_u64(0x0DDB1A5E5BAD5EEDu64))
 }
 
-/// Return a logger suitable for test usage.
-///
-/// By default no logs will be printed, but they can be enabled via the `test_logger` feature.
-///
-/// We've tried the `slog_term::TestStdoutWriter` in the past, but found it too buggy because
-/// of the threading limitation.
-pub fn test_logger() -> Logger {
-    use sloggers::Build;
-
-    if cfg!(feature = "test_logger") {
-        sloggers::terminal::TerminalLoggerBuilder::new()
-            .level(sloggers::types::Severity::Debug)
-            .build()
-            .unwrap()
-    } else {
-        sloggers::null::NullLoggerBuilder.build().unwrap()
-    }
-}
-
 /// Return a `ChainSpec` suitable for test usage.
 ///
 /// If the `fork_from_env` feature is enabled, read the fork to use from the FORK_NAME environment

beacon_node/beacon_chain/src/validator_pubkey_cache.rs

@@ -323,7 +323,8 @@ fn append_to_file(file: &mut File, index: usize, pubkey: &PublicKeyBytes) -> Res
 #[cfg(test)]
 mod test {
     use super::*;
-    use crate::test_utils::{test_logger, BeaconChainHarness, EphemeralHarnessType};
+    use crate::test_utils::{BeaconChainHarness, EphemeralHarnessType};
+    use logging::test_logger;
     use std::sync::Arc;
     use store::{HotColdDB, StoreConfig};
     use tempfile::tempdir;

beacon_node/beacon_chain/tests/block_verification.rs

@@ -4,9 +4,10 @@
 extern crate lazy_static;
 
 use beacon_chain::test_utils::{
-    test_logger, AttestationStrategy, BeaconChainHarness, BlockStrategy, EphemeralHarnessType,
+    AttestationStrategy, BeaconChainHarness, BlockStrategy, EphemeralHarnessType,
 };
 use beacon_chain::{BeaconSnapshot, BlockError, ChainConfig, ChainSegmentResult};
+use logging::test_logger;
 use slasher::{Config as SlasherConfig, Slasher};
 use state_processing::{
     common::get_indexed_attestation,

beacon_node/beacon_chain/tests/store_tests.rs

@@ -3,8 +3,8 @@
 use beacon_chain::attestation_verification::Error as AttnError;
 use beacon_chain::builder::BeaconChainBuilder;
 use beacon_chain::test_utils::{
-    test_logger, test_spec, AttestationStrategy, BeaconChainHarness, BlockStrategy,
-    DiskHarnessType, HARNESS_SLOT_TIME,
+    test_spec, AttestationStrategy, BeaconChainHarness, BlockStrategy, DiskHarnessType,
+    HARNESS_SLOT_TIME,
 };
 use beacon_chain::{
     historical_blocks::HistoricalBlockError, migrate::MigratorConfig, BeaconChain,
@@ -12,6 +12,7 @@ use beacon_chain::{
     WhenSlotSkipped,
 };
 use lazy_static::lazy_static;
+use logging::test_logger;
 use maplit::hashset;
 use rand::Rng;
 use std::collections::HashMap;