Brand new to Pester - should be an array

I am brand new to Pester and cannot for the life of me find any documentation on how to test a variable is of a certain type.

describe 'All Pester Tests' {
it 'gets an array of all webs in the site collection' {
        ## Setup
        Connect-PnPOnline -Url "" -UseWebLogin;
        $allwebs = @();
        ## Positive
        $allwebs.GetType().BaseType | Should -BeOfType "[array]";
        ## Negative
        $allwebs.GetType().BaseType | Should -Not -BeOfType "[string]";

If I do this test manually, I do see my $allwebs is indeed an array

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     Array                                    System.Object

When I run Pester, it fails with

[-] All Pester Tests.gets an array of all webs in the site collection 842ms (842ms|1ms)
 Expected the value to have type [array] or any of its subtypes, but got [array] with type [System.RuntimeType, System.Private.CoreLib, Version=, Culture=neutral, PublicKeyToken=7cec85d7bea7798e].
 at $allwebs.GetType().BaseType | Should -BeOfType "[array]";, C:\Users\jxr4902\gitcloud\ICC-myApronBackendPowerShellApps\tests\ICC-664-Content-Authors-Are-Able-to-Create-Links-Remove-this-ability.Tests.ps1:40
 at <ScriptBlock>, C:\Users\jxr4902\gitcloud\ICC-myApronBackendPowerShellApps\tests\ICC-664-Content-Authors-Are-Able-to-Create-Links-Remove-this-ability.Tests.ps1:40

What is the best way to test a variable for a base type?