Jev

0.4.0

Examples/Demos/Loan-Approval/Get-LoanDecision.Tests.ps1

                                BeforeAll {

    . "$PSScriptRoot/New-LoanApplication.ps1"

    . "$PSScriptRoot/Get-LoanDecision.ps1"

    Import-Module Jev -ErrorAction Stop

}

Describe 'Loan application construction' -Tag Local {

    It 'creates a reusable application with numeric fields' {

        $application = New-LoanApplication -Income 80000 -Requested 20000 -CreditScore 710 -Debt 5000

        $application | Should -BeOfType [pscustomobject]

        $application.Income | Should -Be 80000

        $application.Requested | Should -Be 20000

        $application.CreditScore | Should -Be 710

        $application.Debt | Should -Be 5000

        $application.RequestedPercentIncome | Should -Be 25

        $application.DebtPercentIncome | Should -Be 31.25

        $application.CreditScore = 640

        $application.CreditScore | Should -Be 640

    }

    It 'preserves the calculated percentages for <Case>' -TestCases @(

        @{ Case = 'high debt'; Requested = 30000; Debt = 5000; RequestedPercent = 37.5; DebtPercent = 43.75 }

        @{ Case = 'amount just below half'; Requested = 39999; Debt = 0; RequestedPercent = 49.99875; DebtPercent = 49.99875 }

        @{ Case = 'debt exactly at the limit'; Requested = 20000; Debt = 12000; RequestedPercent = 25; DebtPercent = 40 }

        @{ Case = 'debt just above the limit'; Requested = 20000; Debt = 12001; RequestedPercent = 25; DebtPercent = 40.00125 }

    ) {

        param($Case, $Requested, $Debt, $RequestedPercent, $DebtPercent)

        $application = New-LoanApplication -Income 80000 -Requested $Requested -CreditScore 710 -Debt $Debt

        $application.RequestedPercentIncome | Should -Be ([decimal] $RequestedPercent)

        $application.DebtPercentIncome | Should -Be ([decimal] $DebtPercent)

        $application.RequestedPercentIncome | Should -BeOfType [decimal]

        $application.DebtPercentIncome | Should -BeOfType [decimal]

    }

    It 'refreshes percentages before sending a changed application to Jev' {

        Mock Invoke-Jev { @{ answers = @{ outcome = @{ choice = 'Approve' } } } }

        $application = New-LoanApplication -Income 80000 -Requested 20000 -CreditScore 710 -Debt 5000

        $application.Income = 100000

        $application | Get-LoanDecision | Out-Null

        Should -Invoke Invoke-Jev -Exactly 1 -Scope It -ParameterFilter {

            $State.Income -eq 100000 -and $State.RequestedPercentIncome -eq 20 -and $State.DebtPercentIncome -eq 25

        }

    }

    It 'rejects an invalid edited field before calling Jev' {

        Mock Invoke-Jev { throw 'Invalid application reached Jev.' }

        $application = New-LoanApplication -Income 80000 -Requested 20000 -CreditScore 710 -Debt 5000

        $application.Income = 0

        { $application | Get-LoanDecision } | Should -Throw

        Should -Invoke Invoke-Jev -Exactly 0 -Scope It

    }

    It 'rejects an out-of-range <Field> value of <Value>' -TestCases @(

        @{ Field = 'Income'; Value = 0 }

        @{ Field = 'Income'; Value = 10000001 }

        @{ Field = 'Requested'; Value = 0 }

        @{ Field = 'Requested'; Value = 10000001 }

        @{ Field = 'CreditScore'; Value = 299 }

        @{ Field = 'CreditScore'; Value = 9000 }

        @{ Field = 'Debt'; Value = -1 }

        @{ Field = 'Debt'; Value = 10000001 }

    ) {

        param($Field, $Value)

        $parameters = @{ Income = 80000; Requested = 20000; CreditScore = 710; Debt = 5000 }

        $parameters[$Field] = $Value

        { New-LoanApplication @parameters } | Should -Throw

    }

}

Describe 'Loan decisions against the live Jev model' -Tag Live {

    It 'matches the ordered policy: <Case>' -TestCases @(

        @{ Case = 'approval'; Income = 80000; Requested = 20000; CreditScore = 710; Debt = 5000; Decision = 'Approve'; Reason = 'All approval conditions met' }

        @{ Case = 'amount rule before low credit and high DTI'; Income = 80000; Requested = 40000; CreditScore = 640; Debt = 30000; Decision = 'Deny'; Reason = 'Amount over half of income' }

        @{ Case = 'credit rule before high DTI'; Income = 80000; Requested = 20000; CreditScore = 640; Debt = 20000; Decision = 'Refer'; Reason = 'Credit score below 680' }

        @{ Case = 'high DTI'; Income = 80000; Requested = 30000; CreditScore = 710; Debt = 5000; Decision = 'Deny'; Reason = 'DTI over 0.4' }

        @{ Case = 'credit exactly 680'; Income = 80000; Requested = 20000; CreditScore = 680; Debt = 5000; Decision = 'Approve'; Reason = 'All approval conditions met' }

        @{ Case = 'credit just below 680'; Income = 80000; Requested = 20000; CreditScore = 679; Debt = 5000; Decision = 'Refer'; Reason = 'Credit score below 680' }

        @{ Case = 'amount exactly half'; Income = 80000; Requested = 40000; CreditScore = 710; Debt = 0; Decision = 'Deny'; Reason = 'Amount over half of income' }

        @{ Case = 'amount below half but high DTI'; Income = 80000; Requested = 39999; CreditScore = 710; Debt = 0; Decision = 'Deny'; Reason = 'DTI over 0.4' }

        @{ Case = 'DTI exactly 0.4'; Income = 80000; Requested = 20000; CreditScore = 680; Debt = 12000; Decision = 'Approve'; Reason = 'All approval conditions met' }

        @{ Case = 'DTI just over 0.4'; Income = 80000; Requested = 20000; CreditScore = 710; Debt = 12001; Decision = 'Deny'; Reason = 'DTI over 0.4' }

    ) {

        param($Case, $Income, $Requested, $CreditScore, $Debt, $Decision, $Reason)

        $state = New-LoanApplication -Income $Income -Requested $Requested -CreditScore $CreditScore -Debt $Debt

        $result = Get-LoanDecision -State $state

        $result.Decision | Should -Be $Decision

        $result.Reason | Should -Be $Reason

        $result | Should -BeOfType [pscustomobject]

        @($result.PSObject.Properties.Name) | Should -Be @('Decision', 'Reason')

    }

    It 'changes the decision when only the credit score changes' {

        $state = New-LoanApplication -Income 80000 -Requested 20000 -CreditScore 710 -Debt 5000

        ($state | Get-LoanDecision).Decision | Should -Be 'Approve'

        $state.CreditScore = 640

        ($state | Get-LoanDecision).Decision | Should -Be 'Refer'

        $state.Income | Should -Be 80000

        $state.Requested | Should -Be 20000

        $state.Debt | Should -Be 5000

    }

    It 'returns the expected results for five piped states' {

        $states = @(

            New-LoanApplication -Income 80000 -Requested 20000 -CreditScore 710 -Debt 5000

            New-LoanApplication -Income 80000 -Requested 40000 -CreditScore 640 -Debt 30000

            New-LoanApplication -Income 80000 -Requested 20000 -CreditScore 640 -Debt 20000

            New-LoanApplication -Income 80000 -Requested 30000 -CreditScore 710 -Debt 5000

            New-LoanApplication -Income 80000 -Requested 20000 -CreditScore 680 -Debt 12000

        )

        $results = @($states | Get-LoanDecision)

        $results.Count | Should -Be 5

        $results.Decision | Should -Be @('Approve', 'Deny', 'Refer', 'Deny', 'Approve')

    }

    It 'repeats the same baseline decision with the same model and state' {

        $state = New-LoanApplication -Income 80000 -Requested 20000 -CreditScore 710 -Debt 5000

        $first = $state | Get-LoanDecision

        $second = $state | Get-LoanDecision

        $first.Decision | Should -Be 'Approve'

        $second.Decision | Should -Be $first.Decision

        $second.Reason | Should -Be $first.Reason

    }

}