refactor(GCS): Migrate to using mockery/testify (#25)

* Adds `mockery` generated mocks for `cloudcost-exporter` specific interfaces 
* Removes using mocked interfaces for `pkg/gcp/bucket.go` and favors intercepting HTTP requests 
* Updates uncaught errors for the List commands in `pkg/gcp/bucket.go`

.mockery.yaml

@@ -0,0 +1,11 @@
+with-expecter: True
+inpackage: True
+dir: mocks/{{ replaceAll .InterfaceDirRelative "internal" "internal_" }}
+mockname: "{{.InterfaceName}}"
+outpkg: "{{.PackageName}}"
+filename: "{{.InterfaceName}}.go"
+all: True
+packages:
+  github.com/grafana/cloudcost-exporter:
+    config:
+      recursive: True

go.mod

@@ -48,6 +48,7 @@ require (
 	github.com/matttproud/golang_protobuf_extensions/v2 v2.0.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/prometheus/procfs v0.12.0 // indirect
+	github.com/stretchr/objx v0.5.0 // indirect
 	go.opencensus.io v0.24.0 // indirect
 	go.opentelemetry.io/otel v1.21.0 // indirect
 	go.opentelemetry.io/otel/metric v1.21.0 // indirect

go.sum

@@ -116,6 +116,7 @@ github.com/prometheus/procfs v0.12.0/go.mod h1:pcuDEFsWDnvcgNzo4EEweacyhjeA9Zk3c
 github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/objx v0.5.0 h1:1zr/of2m5FGMsad5YfcqgdqdWrIhu+EBEJRhR1U7z/c=
 github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
 github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=

main.go

@@ -0,0 +1,3 @@
+package cloudcost_exporter
+
+// This is required for mockery to work: https://vektra.github.io/mockery/v2.38/notes/#error-no-go-files-found-in-root-search-path