Help with groovy script

Use

case ~/.*Impact_On_Functioning, outcome=Met.*/:

When you are using "case" with a regex pattern, Groovy will invoke Pattern.isCase(String) method. Looks like the implementation must rely on toString(), while your log statement using ${ } syntax is relying on as String.

String json = '''{
    "criteriaList": [
         {
             "criteriaName": "Impact_On_Functioning",
             "outcome": "Met"
         }
    ]
}'''

def parsedJson = new groovy.json.JsonSlurper().parseText(json)

assert (parsedJson.criteriaList[0] as String) == '[criteriaName:Impact_On_Functioning, outcome:Met]'
assert "${parsedJson.criteriaList[0]}" == (parsedJson.criteriaList[0] as String)
assert parsedJson.criteriaList[0] ==~ ~/.*Impact_On_Functioning, outcome:Met.*/

assert parsedJson.criteriaList[0].toString() == '{criteriaName=Impact_On_Functioning, outcome=Met}'
assert parsedJson.criteriaList[0].toString() ==~ ~/.*Impact_On_Functioning, outcome=Met.*/
assert (~/.*Impact_On_Functioning, outcome=Met.*/).isCase( parsedJson.criteriaList[0] )

switch (parsedJson.criteriaList[0]) {
    case ~/.*Impact_On_Functioning, outcome=Met.*/:
    break
    default:
        assert false
    break
}

Also, consider whether something like this is simpler for you than using Regex at all.

def expectedResults = [
    [criteriaName: "Impact_On_Functioning", outcome: "Met"],
    [criteriaName: "Diagnostic_Determination", outcome: "Met"],
    [criteriaName: "Specialized_Support_Need", outcome: "Met"]
    //...
]

expectedResults.each { assert it in parsedJson.criteriaList }