Add more tests for caliper worker #483

Job	Run time
dci-lint / DCI-Lint	24s
unit-tests / Unit Tests (18.x)	36s
unit-tests / Unit Tests (20.x)	32s
integration-tests / Check for changes	3s
coverage / Coverage Reports (caliper-core)	9s
coverage / Coverage Reports (caliper-fabric)	9s
coverage / Coverage Reports (generator-caliper)	8s
integration-tests / Integration Tests (fabric, 18.x)	13m 48s
integration-tests / Integration Tests (fabric, 20.x)	13m 34s
integration-tests / Integration Tests (ethereum, 18.x)	4m 32s
integration-tests / Integration Tests (ethereum, 20.x)	4m 44s
integration-tests / Integration Tests (besu, 18.x)	6m 41s
integration-tests / Integration Tests (besu, 20.x)	6m 42s
integration-tests / Integration Tests (generator, 18.x)	5m 15s
integration-tests / Integration Tests (generator, 20.x)	5m 29s
	1h 2m 46s

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