feat(entities) Update batch state enum with more states

entity/BUILD.bazel

@@ -18,6 +18,7 @@ go_library(
 go_test(
     name = "entity_test",
     srcs = [
+        "batch_test.go",
         "build_test.go",
         "queue_config_test.go",
         "request_test.go",

entity/batch.go

@@ -6,9 +6,31 @@ type BatchState string
 const (
 	// BatchStateUnknown is the unreachable state. It is set by default when the structure is initialized. It should never be seen in the system.
 	BatchStateUnknown BatchState = ""
-	// TODO: Add comprehensive list of known batch states.
+	// BatchStateCreated is the state of a batch that has been created for processing.
+	BatchStateCreated BatchState = "created"
+	// BatchStateSpeculating is the state of a batch that is undergoing speculative execution.
+	BatchStateSpeculating BatchState = "speculating"
+	// BatchStateFinalizing is the state of a batch that is being finalized after speculative execution.
+	BatchStateFinalizing BatchState = "finalizing"
+	// BatchStateSucceeded is the terminal state of a batch that has been successfully landed.
+	BatchStateSucceeded BatchState = "succeeded"
+	// BatchStateFailed is the terminal state of a batch that has failed.
+	BatchStateFailed BatchState = "failed"
+	// BatchStateCancelled is the terminal state of a batch that was cancelled before completion.
+	BatchStateCancelled BatchState = "cancelled"
 )
 
+// IsTerminal returns true if the batch state is a terminal state.
+// Terminal states are states from which no further transitions are possible.
+func (s BatchState) IsTerminal() bool {
+	switch s {
+	case BatchStateSucceeded, BatchStateFailed, BatchStateCancelled:
+		return true
+	default:
+		return false
+	}
+}
+
 // Batch represents a group of requests to land (merge into target branch of the source control repository).
 type Batch struct {
 	// ID is the globally unique identifier for the batch. Format: "<queue>/batch/<counter_value>".

entity/batch_test.go

@@ -0,0 +1,30 @@
+package entity
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestBatchState_IsTerminal(t *testing.T) {
+	tests := []struct {
+		name     string
+		state    BatchState
+		terminal bool
+	}{
+		{name: "unknown", state: BatchStateUnknown, terminal: false},
+		{name: "created", state: BatchStateCreated, terminal: false},
+		{name: "speculating", state: BatchStateSpeculating, terminal: false},
+		{name: "finalizing", state: BatchStateFinalizing, terminal: false},
+		{name: "succeeded", state: BatchStateSucceeded, terminal: true},
+		{name: "failed", state: BatchStateFailed, terminal: true},
+		{name: "cancelled", state: BatchStateCancelled, terminal: true},
+		{name: "arbitrary string", state: BatchState("something_else"), terminal: false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.terminal, tt.state.IsTerminal())
+		})
+	}
+}