feat: add command domain invariants

internal/domain/revision_test.go

@@ -0,0 +1,47 @@
+package domain
+
+import (
+	"errors"
+	"math"
+	"testing"
+)
+
+func TestRevisionComparisonAndAdvance_HP_CMD_01(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name     string
+		current  CommandRevision
+		incoming CommandRevision
+		want     RevisionRelation
+		wantErr  error
+	}{
+		{"zero current", 0, 1, RevisionInvalid, ErrInvalidRevision},
+		{"zero incoming", 1, 0, RevisionInvalid, ErrInvalidRevision},
+		{"stale", 4, 3, RevisionStale, ErrStaleRevision},
+		{"current", 4, 4, RevisionCurrent, nil},
+		{"future", 4, 5, RevisionFuture, ErrFutureRevision},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			if got := CompareRevision(test.current, test.incoming); got != test.want {
+				t.Fatalf("CompareRevision() = %v, want %v", got, test.want)
+			}
+			err := ValidateCurrentRevision(test.current, test.incoming)
+			if !errors.Is(err, test.wantErr) {
+				t.Fatalf("ValidateCurrentRevision() error = %v, want %v", err, test.wantErr)
+			}
+		})
+	}
+
+	if next, err := NextRevision(InitialCommandRevision); err != nil || next != 2 {
+		t.Fatalf("NextRevision(1) = (%d, %v), want (2, nil)", next, err)
+	}
+	if _, err := NextRevision(0); !errors.Is(err, ErrInvalidRevision) {
+		t.Fatalf("NextRevision(0) error = %v", err)
+	}
+	if _, err := NextRevision(math.MaxUint64); !errors.Is(err, ErrRevisionOverflow) {
+		t.Fatalf("NextRevision(max) error = %v", err)
+	}
+}