make test fails when gotestsum is installed

[cuminandpaprika]

Description

running make test fails when gotestsum is installed.

Further investigation shows that running go test --json ./... produces a failing output:

{"Time":"2020-03-18T16:56:08.651278+11:00","Action":"fail","Package":"github.com/anz-bank/sysl/cmd/sysl","Test":"TestMain3","Elapsed":0.5}

Steps to Reproduce

1. Checkout master branch
2. run make test with gotestsum installed

Expected behavior:
All tests should pass as running go test ./... passes

Actual behavior:
Test fails, output shown below

• Debug&Crash Output
  Using gotestsum installed via go get gotest.tools/gotestsum
  go version go1.13.8 darwin/amd64 from commit hash: gotestyourself/gotestsum@b9c9035

=== Failed
=== FAIL: cmd/sysl TestMain3 (0.54s)
usage: sysl [<flags>] <command> [<args> ...]
System Modelling Language Toolkit
Optional flags:
      --help        Show context-sensitive help (also try --help-long and
                    --help-man).
      --version     Show application version.
      --log="warn"  log level: [trace,off,debug,info,warn]
  -v, --verbose     enable verbose logging
      --root=ROOT   sysl root directory for input model file. If root is not
                    found, the module directory becomes the root, but the module
                    can not import with absolute paths (or imports must be
                    relative).
Commands:
  help [<command>...]
    Show help.
  codegen --transform=TRANSFORM --grammar=GRAMMAR [<flags>] <MODULE>...
    Generate code
  datamodel [<flags>] <MODULE>...
    Generate data models
  env
    Print sysl environment information.
  export [<flags>] <MODULE>...
    Export sysl to external types. Supported types: Swagger
  generate-db-scripts [<flags>] <MODULE>...
    Generate db script
  generate-db-scripts-delta [<flags>] <MODULE>...
    Generate delta db scripts
  import --input=INPUT --app-name=APP-NAME [<flags>]
    Import foreign type to sysl. Supported types: [grammar, openapi, swagger,
    xsd]
  info
    Show binary information
  integrations [<flags>] <MODULE>...
    Generate integrations
  mod init [<name>]
    initializes and writes a new go.mod to the current directory
  protobuf [<flags>] <MODULE>...
    Generate textpb/json
  repl
    Enter a sysl REPL
  sd [<flags>] <MODULE>...
    Generate Sequence Diagram
  template --template=TEMPLATE --start=START [<flags>] <MODULE>...
    Apply a model to a template for custom text output
  test-rig --template=TEMPLATE [<flags>] <MODULE>...
    Generate test rig
  ui [<flags>] <MODULE>...
    Starts the Sysl UI which displays a visual view of Apps defined in the sysl
    model.
  validate <MODULE>...
    Validate the sysl file
ok  	github.com/anz-bank/sysl/cmd/sysl	0.526s
DONE 979 tests, 1 failure in 6.255s