Cannot convert value "System.String" to type "System.Boolean"

[JaeEmAre67]

Brand new to Pester.

Describe "Get timestamp for output file" {
It "returns <expected> (param)" -TestCases @(
@{ Param = "$true $true"; Expected = Get-Date -Format "yyyyMMddHHmm" }
@{ Param = "$true $false"; Expected = Get-Date -Format "yyyyMMdd" }
@{ Param = "$false $true"; Expected = Get-Date -Format "HHmm" }
@{ Param = "$false $false"; Expected = Get-Date -Format "yyyyMMdd" }
@{ Param = ""; Expected = Get-Date -Format "yyyyMMdd" }
) {
get-util-timeStamp $param | Should -Be $expected;
}
}

In the errors I can see it is indeed returning the date in the specified format, however all are failing with the error:
PSInvalidCastException: Cannot convert value "System.String" to type "System.Boolean". Boolean parameters accept only Boolean values and numbers, such as $True, $False,
1 or 0.
ArgumentTransformationMetadataException: Cannot convert value "System.String" to type "System.Boolean". Boolean parameters accept only Boolean values and numbers, such as $True, $False, 1 or 0.
ParameterBindingArgumentTransformationException: Cannot process argument transformation on parameter 'date'. Cannot convert value "System.String" to type "System.Boolean". Boolean parameters accept only Boolean values and numbers, such as $True, $False,
1 or 0.
at , c:\myapp\tests\utils.Tests.ps1:13

Which would make a bit of sense to me if it wasn't returning the expected value
[-] Get timestamp for output file.returns 202109201037 22ms (18ms|4ms)
[-] Get timestamp for output file.returns 20210920 3ms (2ms|1ms)
[-] Get timestamp for output file.returns 1037 2ms (1ms|1ms)
[-] Get timestamp for output file.returns 20210920 2ms (2ms|1ms)
[-] Get timestamp for output file.returns 20210920 2ms (1ms|1ms)

Can anyone please advise where I'm wrong?

[fflaten]

It's not Pester that's complaining about Expected, it is your function complaining about the input. Your function probably expects one or two bool-parameters but you give it a single string.

You're effectively running get-util-timeStamp "True True". "True True" can't be converted to bool