Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/bs-logger/dist/testing/index.d.ts

@@ -0,0 +1,8 @@
+import { CreateLoggerOptions, Logger } from '../logger';
+import { ExtendedArray, LogTargetMock, extendArray } from './target-mock';
+declare const setupForTesting: (target?: LogTargetMock) => void;
+interface LoggerMock extends Logger {
+    readonly target: LogTargetMock;
+}
+declare const createLoggerMock: (options?: CreateLoggerOptions | undefined, target?: LogTargetMock) => LoggerMock;
+export { LogTargetMock, ExtendedArray, extendArray, setupForTesting as setup, createLoggerMock, LoggerMock };