Add longest chain tests and test vectors.

eth2/fork_choice/tests/longest_chain_test_vectors.yaml

@@ -0,0 +1,51 @@
+title: Fork-choice Tests
+summary: A collection of abstract fork-choice tests to verify the longest chain fork-choice rule.
+test_suite: Fork-Choice
+
+test_cases:
+- blocks:
+    - id: 'b0'
+      parent: 'b0'
+    - id: 'b1'
+      parent: 'b0'
+    - id: 'b2'
+      parent: 'b1'
+    - id: 'b3'
+      parent: 'b1'
+    - id: 'b4'
+      parent: 'b3'
+  weights:
+    - b0: 0
+    - b1: 0
+    - b2: 10
+    - b3: 1
+  heads:
+    - id: 'b4'
+- blocks:
+    - id: 'b0'
+      parent: 'b0'
+    - id: 'b1'
+      parent: 'b0'
+    - id: 'b2'
+      parent: 'b1'
+    - id: 'b3'
+      parent: 'b2'
+    - id: 'b4'
+      parent: 'b3'
+    - id: 'b5'
+      parent: 'b0'
+    - id: 'b6'
+      parent: 'b5'
+    - id: 'b7'
+      parent: 'b6'
+    - id: 'b8'
+      parent: 'b7'
+    - id: 'b9'
+      parent: 'b8'
+  weights:
+    - b0: 5
+    - b1: 20
+    - b2: 10
+    - b3: 10
+  heads:
+    - id: 'b9'

eth2/fork_choice/tests/tests.rs

@@ -45,6 +45,16 @@ fn test_slow_lmd_ghost() {
     );
 }
 
+#[test]
+fn test_longest_chain() {
+    test_yaml_vectors(
+        ForkChoiceAlgorithm::LongestChain,
+        "tests/longest_chain_test_vectors.yaml",
+        100,
+        "debug",
+    );
+}
+
 // run a generic test over given YAML test vectors
 fn test_yaml_vectors(
     fork_choice_algo: ForkChoiceAlgorithm,