public String expectFileString(String file) {
        return expectFileString(Paths.get(file));
    }
Expects that the given file was stored and returns a UTF-8 string.

@param file File to retrieve.
@return Returns the bytes of the file if found.
@throws InvalidPathException if the file cannot be found.
smithy-build/src/main/java/software/amazon/smithy/build/MockManifest.java