withCopyFile method
Copies the file at hostPath to containerPath in the container
before it starts. A relative hostPath starts at the working
directory (the package, under dart test); the file is read at
start. mode is the permission (0644 by default, as 0x1A4).
Implementation
GenericContainer withCopyFile(
String hostPath,
String containerPath, {
int mode = 420,
}) {
_copies.add(_Copy(containerPath, mode, hostPath: hostPath));
return this;
}