diff --git a/beacon_node/beacon_chain/test_harness/README.md b/beacon_node/beacon_chain/test_harness/README.md
new file mode 100644
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+# Test Harness
+
+Provides a testing environment for the `BeaconChain`, `Attester` and `BlockProposer` objects.
+
+This environment bypasses networking and client run-times and connects the `Attester` and `Proposer`
+directly to the `BeaconChain` via an `Arc`.
+
+The `BeaconChainHarness` contains a single `BeaconChain` instance and many `ValidatorHarness`
+instances. All of the `ValidatorHarness` instances work to advance the `BeaconChain` by
+producing blocks and attestations.
+
+The crate consists of a library and binary, examples for using both are
+described below.
+
+## YAML
+
+Both the library and the binary are capable of parsing tests from a YAML file,
+in fact this is the sole purpose of the binary.
+
+You can find YAML test cases [here](specs/). An example is included below:
+
+```yaml
+title: Validator Registry Tests
+summary: Tests deposit and slashing effects on validator registry.
+test_suite: validator_registry
+fork: tchaikovsky
+version: 1.0
+test_cases:
+  - config:
+      epoch_length: 64
+      deposits_for_chain_start: 1000
+      num_slots: 64
+      skip_slots: [2, 3]
+      deposits:
+          # At slot 1, create a new validator deposit of 32 ETH.
+        - slot: 1
+          amount: 32
+          # Trigger more deposits...
+        - slot: 3
+          amount: 32
+        - slot: 5
+          amount: 32
+      proposer_slashings:
+          # At slot 2, trigger a proposer slashing for validator #42.
+        - slot: 2
+          validator_index: 42
+          # Trigger another slashing...
+        - slot: 8
+          validator_index: 13
+      attester_slashings:
+          # At slot 2, trigger an attester slashing for validators #11 and #12.
+        - slot: 2
+          validator_indices: [11, 12]
+          # Trigger another slashing...
+        - slot: 5
+          validator_indices: [14]
+    results:
+      num_skipped_slots: 2
+      states:
+        - slot: 63
+          num_validators: 1003
+          slashed_validators: [11, 12, 13, 14, 42]
+          exited_validators: []
+
+```
+
+Thanks to [prsym](http://github.com/prysmaticlabs/prysm) for coming up with the
+base YAML format.
+
+### Notes
+
+Wherever `slot` is used, it is actually the "slot height", or slots since
+genesis. This allows the tests to disregard the `GENESIS_EPOCH`.
+
+### Differences from Prysmatic's format
+
+1. The detail for `deposits`, `proposer_slashings` and `attester_slashings` is
+   ommitted from the test specification. It assumed they should be valid
+   objects.
+2. There is a `states` list in `results` that runs checks against any state
+   specified by a `slot` number. This is in contrast to the variables in
+   `results` that assume the last (highest) state should be inspected.
+
+#### Reasoning
+
+Respective reasonings for above changes:
+
+1. This removes the concerns of the actual object structure from the tests.
+   This allows for more variation in the deposits/slashings objects without
+   needing to update the tests. Also, it makes it makes it easier to create
+   tests.
+2. This gives more fine-grained control over the tests. It allows for checking
+   that certain events happened at certain times whilst making the tests only
+   slightly more verbose.
+
+_Notes: it may be useful to add an extra field to each slashing type to
+indicate if it should be valid or not. It also may be useful to add an option
+for double-vote/surround-vote attester slashings. The `amount` field was left
+on `deposits` as it changes the behaviour of state significantly._
+
+## Binary Usage Example
+
+Follow these steps to run as a binary:
+
+1. Navigate to the root of this crate (where this readme is located)
+2. Run `$ cargo run --release -- --yaml examples/validator_registry.yaml`
+
+_Note: the `--release` flag builds the binary without all the debugging
+instrumentation. The test is much faster built using `--release`. As is
+customary in cargo, the flags before `--` are passed to cargo and the flags
+after are passed to the binary._
+
+### CLI Options
+
+```
+Lighthouse Test Harness Runner 0.0.1
+Sigma Prime <contact@sigmaprime.io>
+Runs `test_harness` using a YAML test_case.
+
+USAGE:
+    test_harness --log-level <LOG_LEVEL> --yaml <FILE>
+
+FLAGS:
+    -h, --help       Prints help information
+    -V, --version    Prints version information
+
+OPTIONS:
+        --log-level <LOG_LEVEL>    Logging level. [default: debug]  [possible values: error, warn, info, debug, trace]
+        --yaml <FILE>              YAML file test_case.
+```
+
+
+## Library Usage Example
+
+```rust
+use test_harness::BeaconChainHarness;
+use types::ChainSpec;
+
+let validator_count = 8;
+let spec = ChainSpec::few_validators();
+
+let mut harness = BeaconChainHarness::new(spec, validator_count);
+
+harness.advance_chain_with_block();
+
+let chain = harness.chain_dump().unwrap();
+
+// One block should have been built on top of the genesis block.
+assert_eq!(chain.len(), 2);
+```
diff --git a/beacon_node/beacon_chain/test_harness/src/lib.rs b/beacon_node/beacon_chain/test_harness/src/lib.rs
index 2303dc064..0703fd4a5 100644
--- a/beacon_node/beacon_chain/test_harness/src/lib.rs
+++ b/beacon_node/beacon_chain/test_harness/src/lib.rs
@@ -1,6 +1,6 @@
 //! Provides a testing environment for the `BeaconChain`, `Attester` and `BlockProposer` objects.
 //!
-//! This environment bypasses networking client runtimes and connects the `Attester` and `Proposer`
+//! This environment bypasses networking and client run-times and connects the `Attester` and `Proposer`
 //! directly to the `BeaconChain` via an `Arc`.
 //!
 //! The `BeaconChainHarness` contains a single `BeaconChain` instance and many `ValidatorHarness`