Cellular: fixed athandler unit tests.

[jarvte]

Description

Fixed ATHandler unit tests. No code changes.

Internal ref to defect: IOTCELL-777

Pull request type

[X] Fix
[ ] Refactor
[ ] New target
[ ] Feature
[ ] Breaking change

[AnttiKauppila]

I don't like magic number 20, but if we create more tests needing different values, we can stub it then.

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 1741
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6620/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1375
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6620/

[mbed-ci]

Test : FAILURE

Build number : 1544
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6620/1544

[cmonr]

Interesting. Second occurance of Echo test failing with EV_COG_AD4050LZ board when compiled with IAR.

/morph test

[mbed-ci]

Test : SUCCESS

Build number : 1554
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6620/1554