Format JSON data With Dot Notation for Jest Mock

I have an input field that reads a value from an api property. Everything works fine except when I try to write a test Test to mock the data. I am assuming that I must be making some kind of mistake in my formatting.

The fields in question grab a a value from an object passed in via a public property. When I try to run a Jest test I get an error that

<template if:true={dataLoaded}>
        <div class="screen">         
                <lightning-input label="Parent First Name"
                                 type="text"
                                 value={patient.LegalGuardian__r.FirstName}
                                 onchange={handleChange}
                                 name="firstName"
                                 required
                                 data-id="parentFirstName">
                </lightning-input>
                <lightning-input label="Parent Last Name"
                                 value={patient.LegalGuardian__r.LastName}
                                 onchange={handleChange}
                                 name="lastName"
                                 required
                                 type="text"
                                 data-id="parentLastName">
                </lightning-input>
                <lightning-input label={labels.parentVerificationText}
                                 class="slds-required"
                                 required
                                 type="Checkbox">
                </lightning-input>

        </div>
 </template>

Mock JSON file

{
  "FirstName": "Adult",
  "LastName": "Patient",
  "LegalGuardian__r.FirstName": "test",
  "LegalGuardian__r.LastName": "Guardian",
  "RecordTypeId": "01209000000IlhyAAC",
  "LanguagePreference__pc": "English",
  "Age__pc": 50,
  "Id": "0017Z00001WcRoPQAV",
  "RecordType": {
    "Id": "01209000000IlhyAAC"
  }
}

This works just fine in practice. But whenI try to pass a JSON file to the API in a Jest test I will get errors that that the properties FirstName and LastName are undefined. I tried to pass it with JSON.parse() but that did not solve it. Is there some way to format the JSON so that it works in my tests when passed as a public property?

I have expirmented with trying to return the value with a getter to help with testing. But the test still throws the same error.

get guardianLastName() {
    return this.patient.LegalGuardian__r.LastName !== undefined
      ? this.patient.LegalGuardian__r.LastName
      : '';
  }