testing: add robust source testing

Author: knudtty

packages/api/src/models/source.ts

@@ -128,5 +128,6 @@ export const SessionSource = Source.discriminator<
  SourceKind.Session,
  new mongoose.Schema<Extract<TSource, { kind: SourceKind.Session }>>({
  traceSourceId: String,
+ timestampValueExpression: String,
  }),
 );