steps:

1. EXEC: Ctrl + 3 and provide "Runtime" into the filter field, choose Download Runtimes
2. EXEC: choose CDK v3.3.0, hit "Next"
3. ASSERT: credentials page shows up
4. EXEC: provide credentials, hit "Next"
5. ASSERT: license page shows up
6. EXEC: accept it, hit "Next"
7. ASSERT: "Download Runtime" page shows up
8. EXEC: confirm suggested values, hit "Finish"
9. ASSERT: download is triggered, is progressing.

Result:
Once the download is finished, an error shows up:

If you verify the destination, you see that it's actually a file (while the dialog talks of a folder):

$ ls -l cdk-3.3.0-1-minishift-darwin-amd64
-rwxr--r--  1 adietish  staff   461M Mar 21 14:52 cdk-3.3.0-1-minishift-darwin-amd64