Powershell Not saving Value - powershell

Question

I have a question about my code.
I realize a form in powershell and when i click on the button, The code add in the datagridview the variable $Test, if checkbox is checked and $test = YES. After the first action on the button, I change the variable $test to "NO".
But when I click again on the button, the variable $Test is again to "YES" ... and I don't understand why the variable is reset to YES and not saved with the new value "NO"
Example :
[reflection.assembly]::loadwithpartialname("System.Windows.Forms") | Out-Null
[reflection.assembly]::loadwithpartialname("System.Drawing") | Out-Null
$Test = "YES"
Add-Type -AssemblyName System.Windows.Forms
Add-Type -AssemblyName System.Drawing
$MyForm = New-Object System.Windows.Forms.Form
$MyForm.Text="test"
$MyForm.Size = New-Object System.Drawing.Size(1000,350)
$mButton1 = New-Object System.Windows.Forms.Button
$mButton1.Text="test"
$mButton1.Top="155"
$mButton1.Left="30"
$mButton1.Anchor="Left,Top"
$mButton1.Size = New-Object System.Drawing.Size(100,23)
$MyForm.Controls.Add($mButton1)
$mButton1.Add_Click({
If($mCheckBox4.Checked -eq $True -and $Test -eq "YES"){
write-host "IN IF"$Test
$DataGridView.Rows.Add($Test)
}
$Test = "NO"
write-host "Out IF"$Test
})
$mCheckBox4 = New-Object System.Windows.Forms.CheckBox
$mCheckBox4.Text="test"
$mCheckBox4.Top="80"
$mCheckBox4.Left="10"
$mCheckBox4.Anchor="Left,Top"
$mCheckBox4.Size = New-Object System.Drawing.Size(100,23)
$MyForm.Controls.Add($mCheckBox4)
$dataGridView = New-Object System.Windows.Forms.DataGridView
$dataGridView.RowTemplate.DefaultCellStyle.ForeColor = [System.Drawing.Color]::FromArgb(255,0,128,0)
$dataGridView.Name = 'dataGridView'
$dataGridView.DataBindings.DefaultDataSourceUpdateMode = 0
$dataGridView.ReadOnly = $True
$dataGridView.Top="5"
$dataGridView.Left="500"
$dataGridView.Size = New-Object System.Drawing.Size(425,185)
$dataGridView.AllowUserToDeleteRows = $False
$dataGridView.RowHeadersVisible = $False
#$dataGridView.TabIndex = 8
$dataGridView.SelectionMode = 'FullRowSelect'
#$dataGridView.Anchor = 15
$dataGridView.AutoSizeColumnsMode = 16
$dataGridView.AllowUserToAddRows = $False
#$dataGridView.ColumnHeadersHeightSizeMode = 2
#$dataGridView.AllowUserToOrderColumns = $True
#$dataGridView.AllowUserToResizeRows = $False
$dataGridView.ColumnCount = 1
$dataGridView.ColumnHeadersVisible = $true
$dataGridView.Columns[0].Name = "Trigger"
$MyForm.Controls.Add($dataGridView)
$MyForm.ShowDialog()
https://www.hostingpics.net/viewer.php?id=8107302017081612h0222.png
In this pictures, i add a write-host to see the value of my variable $Test, and he switch into "YES/NO" "YES/NO" ...
Thanks for your help
Regards