Introduction to Pester – Part 1

Let’s create your first Pester test. We will look at the first example here. We will break this down into a few parts. Let’s suppose that you need to test a script created to perform certain tasks in Office 365. This will require you to connect PowerShell to your Office 365 tenant. Please check this link to download the EXO V2 PowerShell Module.

Use these commands to connect to Office 365 tenant:

$Credentials = Get-Credential
Connect-ExchangeOnline -Credential $Credentials

You have a csv file with the list of the users on whom you need to perform your tasks. The first aim would be to ensure that the path that’s provided does actually exist. Let’s create a test to verify that.

Describe "Test-CSV" {
It "CSV exists" {
"" | Should -Exist
}
}

If the file exists in the said location, then the output should resemble this:

Fig. 2: Successful path test

There are quite a few things happening here. First thing is, we used the Invoke-Pester command to start the Pester test. This is the way to call upon a test.

The next part is to discover the test file on the given location. Pester tests have this format “filename.tests.ps1″.

Tip: ScriptRunner automatically recognizes Pester tests by their file format. The corresponding test scripts are automatically filed in the “Pester Tests” sublibrary of the ScriptRunner Admin App.

ScriptRunner automatically sorts Pester scripts in the “Pester Tests” sublibrary.

Once the file is found it would check the number of conditions given and then perform the test. The test result is then displayed at the bottom.

In this case, I had created the file at the location mentioned; hence, my test was successful. However, if the file isn’t found at that location, the output would be as shown in figure 3:

Fig. 3: Unsuccessful Path Test

The other aspects of this test are the ‘Describe’ and ‘It’ blocks. You will read more about them in the next section.

The functions used in Pester are easy to grasp as seen in the example discussed earlier. The blocks used in Pester are:

• Describe
• It
• Context
• BeforeAll
• AfterAll
• BeforeEach
• AfterEach

The It block is where you state your conditions against which the test shall run. As seen in the example above, we provided the condition that the usage location of the mailbox must be “India” in the first It block.

The 2nd It block had the condition that the usage location must not be “United Kingdom”.

The result of the test can be one of the following:

• Passed – All the conditions in the test passed.
• Failed – The result did not meet the conditions set by us.
• Skipped – The test was skipped.
• Pending – The test could not be run as its pending or empty.
• Inconclusive – Result of the test was neither passed nor failed.

In our example the 1st It block test passed, whereas the 2nd one failed (figure 4).

Fig. 4: It block test output

The Describe block groups all the tests within it. However, if a test needs to be run in different conditions or circumstances, you can use the Context block. This block is similar to the Describe block; however, there are a few significant differences.

The Context block will exist within the Describe block. There can even be multiple Context blocks in one Describe block: As the name suggests, you could use them to divide your tests in different contexts.

In the example here, you will notice that I have added 2 Context blocks to differentiate between the tests for usage location and address book. Here’s the code:

Context "Check Usage Location" {
It "Check if India" -Tag "India" {
Get-UsageLocation "yogi@testdomain1988.onmicrosoft.com" | Should -Be "India"
}
It "Usage location should not be UK" -Tag "NotUK" {
Get-UsageLocation "derek@testdomain1988.onmicrosoft.com" | Should -Not -Be "United Kingdom"
}
}
#end of usagelocation context
Context "Is it hidden from the address book" -Tag HiddenFromGAL {
It "Check hidden from GAL attribute" {
Get-HiddenFromGal "vignesh@testdomain1988.onmicrosoft.com" | Should -Be "False"
}
} #end of Hidden from GAL context block

You might want to run some specific tasks or codes at the beginning. In our example, there are 2 functions at present which need to be referred to later in the script. One option is to use the BeforeAll block to save the 2 functions in memory.
This block is run before any of the It blocks.
You can now add the functions within the BeforeAll block as shown here:

BeforeAll {
#Connecting to Exchange Online PowerShell Module
. #Functions
function Get-UsageLocation ($User){
return (Get-Mailbox $User).UsageLocation
}
function Get-HiddenFromGal ($Account){
return (Get-Mailbox $Account).HiddenFromAddressListsEnabled
}
}

Running the test now clearly shows that its functioning as expected (see figure 5).

Fig. 5: BeforeAll test output

In certain situations, you might want to perform a set of tasks at the end of a test or block. Hence, it’s run after the execution of all the It blocks.

Adding the following code block at the end of the last It block will ensure that the Exchange Online PowerShell session is disconnected after the tests have run:

AfterAll{
Disconnect-ExchangeOnline -Confirm:$false
}

The BeforeEach and AfterEach blocks come in handy when you wish a certain code block to be executed before and after every It block. You can use it to make an entry to a log file or to even display something in the PowerShell result.

In the example that we have been building on in this session, I have used the BeforeEach and AfterEach blocks to show a text in the result:

BeforeEach {
Write-Host "BeforeEach Block" -BackgroundColor DarkMagenta
}
AfterEach {
Write-Host "AfterEach Block" -BackgroundColor Black
}