Updated Pester Syntax in Writing Tests Guide (#8039)
- Modified the Pester syntax for the `-Be` assertion (instead of just `Be`) to reflect the preferred use per latest version of Pester. - Added an example showing use of `-BeOfType` to test the type of a variable. - Other minor changes for grammar.
This commit is contained in:
Mark Wragg
Travis Plunk
parent
a4d4c31390
commit
8215914b46
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@ -1,12 +1,11 @@
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### Writing Pester Tests
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Note that this document does not replace the documents found in the [Pester](https://github.com/pester/pester "Pester") project.
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This is just some quick tips and suggestions for creating Pester tests for this project.
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The Pester community is vibrant and active, if you have questions about Pester or creating tests, the [Pester Wiki](https://github.com/pester/pester/wiki) has a lot of great information.
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As of January 2018, PowerShell Core is using Pester version 4 which has some changes from earlier versions.
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See [Migrating from Pester 3 to Pester 4](https://github.com/pester/Pester/wiki/Migrating-from-Pester-3-to-Pester-4) for more information.
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When creating tests, keep the following in mind:
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* Tests should not be overly complicated and test too many things
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* boil down your tests to their essence, test only what you need
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@ -14,28 +13,29 @@ When creating tests, keep the following in mind:
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* Tests should generally not rely on any other test
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Examples:
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Here's the simplest of tests
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Here's the simplest of tests:
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```powershell
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Describe "A variable can be assigned and retrieved" {
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It "Create a variable and make sure its value is correct" {
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It "Creates a variable and makes sure its value is correct" {
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$a = 1
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$a | Should Be 1
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$a | Should -Be 1
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}
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}
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```
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If you need to do type checking, that can be done as well
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If you need to do type checking, that can be done as well:
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```powershell
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Describe "One is really one" {
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It "Compare 1 to 1" {
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$a = 1
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$a | Should Be 1
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$a | Should -Be 1
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}
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It "1 is really an int" {
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$i = 1
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$i.GetType() | Should Be "int"
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$i.GetType() | Should -BeExactly "int"
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}
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}
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```
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@ -46,11 +46,11 @@ alternatively, you could do the following:
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Describe "One is really one" {
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It "Compare 1 to 1" {
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$a = 1
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$a | Should Be 1
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$a | Should -Be 1
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}
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It "1 is really an int" {
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$i = 1
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$i.GetType() | Should Be ([System.Int32])
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$i | Should -BeOfType System.Int32
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}
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}
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```
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@ -65,7 +65,7 @@ It "Get-Item on a nonexisting file should have error PathNotFound" {
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}
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```
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Note that if Get-Item were to succeed, the test will fail.
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Note that if `Get-Item` were to succeed, the test will fail.
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However, if you need to check the `InnerException` or other members of the ErrorRecord, you should use `-PassThru` parameter:
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@ -73,43 +73,52 @@ However, if you need to check the `InnerException` or other members of the Error
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It "InnerException sample" {
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$e = { Invoke-WebRequest https://expired.badssl.com/ } | Should -Throw -ErrorId "WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeWebRequestCommand" -PassThru
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$e.Exception.InnerException.NativeErrorCode | Should Be 12175
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$e.Exception.InnerException.NativeErrorCode | Should -Be 12175
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...
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}
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```
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### Describe/Context/It
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For creation of PowerShell tests, the Describe block is the level of granularity suggested and one of three tags should be used: "CI", "Feature", or "Scenario". If the tag is not provided, tests in that describe block will be run any time tests are executed.
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For creation of PowerShell tests, the `Describe` block is the level of granularity suggested and one of three tags should be used: "CI", "Feature", or "Scenario". If the tag is not provided, tests in that describe block will be run any time tests are executed.
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#### Describe
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Creates a logical group of tests. All Mocks and TestDrive contents defined within a Describe block are scoped to that Describe; they will no longer be present when the Describe block exits. A `Describe block may contain any number of Context and It blocks.
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Creates a logical group of tests.
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All `Mocks` and `TestDrive` contents defined within a `Describe` block are scoped to that `Describe`;
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they will no longer be present when the `Describe` block exits.
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A `Describe` block may contain any number of Context and `It` blocks.
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#### Context
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Provides logical grouping of It blocks within a single Describe block. Any Mocks defined inside a Context are removed at the end of the Context scope, as are any files or folders added to the TestDrive during the Context block's execution. Any BeforeEach or AfterEach blocks defined inside a Context also only apply to tests within that Context .
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Provides logical grouping of `It` blocks within a single `Describe` block. Any Mocks defined inside a `Context` are removed at the end of the `Context` scope, as are any files or folders added to the `TestDrive:` during the Context block's execution. Any `BeforeEach` or `AfterEach` blocks defined inside a `Context` also only apply to tests within that `Context`.
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#### It
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The It block is intended to be used inside of a Describe or Context Block. If you are familiar with the AAA pattern (Arrange-Act-Assert), the body of the It block is the appropriate location for an assert. The convention is to assert a single expectation for each It block. The code inside of the It block should throw a terminating error if the expectation of the test is not met and thus cause the test to fail. The name of the It block should expressively state the expectation of the test.
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The `It` block is intended to be used inside of a `Describe` or `Context` block. If you are familiar with the AAA pattern (Arrange-Act-Assert), the body of the `It` block is the appropriate location for an assert. The convention is to assert a single expectation for each `It` block. The code inside of the `It` block should throw a terminating error if the expectation of the test is not met and thus cause the test to fail. The name of the `It` block should expressively state the expectation of the test.
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### Admin privileges in tests
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Tests that require admin privileges **on windows** should be additionally marked with 'RequireAdminOnWindows' Pester tag.
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Tests that require admin privileges **on Windows** must be additionally marked with `RequireAdminOnWindows` Pester tag.
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In the AppVeyor CI, we run two different passes:
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- The pass with exclusion of tests with 'RequireAdminOnWindows' tag
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- The pass where we run only 'RequireAdminOnWindows' tests
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- The pass with exclusion of tests with `RequireAdminOnWindows` tag
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- The pass where we run only `RequireAdminOnWindows` tests
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In each case, tests are executed with appropriate privileges.
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Tests that need to be run with sudo **on Unix systems** should be additionally marked with 'RequireSudoOnUnix' Pester tag.
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'RequireSudoOnUnix' tag is mutually exclusive to all other tags like 'CI', 'Feature' etc. (which are now ignored when 'RequireSudoOnUnix' is present) and is treated as 'CI'.
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Tests that need to be run with sudo **on Unix systems** must be additionally marked with `RequireSudoOnUnix` Pester tag.
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`RequireSudoOnUnix` tag is mutually exclusive to all other tags like `CI`, `Feature` etc. (which are now ignored when `RequireSudoOnUnix` is present) and is treated as `CI`.
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Similarly as above, we run the tests in Travis CI in two passes:
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- With sudo only tests with 'RequireSudoOnUnix' tag
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- Without sudo all tests excluding those with 'RequireSudoOnUnix' tag.
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- With sudo only tests with `RequireSudoOnUnix` tag
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- Without sudo all tests excluding those with `RequireSudoOnUnix` tag.
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### Selected Features
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#### Test Drive
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A PSDrive is available for file activity during a tests and this drive is limited to the scope of a single Describe block. The contents of the drive are cleared when a context block is exited.
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A test may need to work with file operations and validate certain types of file activities. It is usually desirable not to perform file activity tests that will produce side effects outside of an individual test. Pester creates a PSDrive inside the user's temporary drive that is accessible via a names PSDrive TestDrive:. Pester will remove this drive after the test completes. You may use this drive to isolate the file operations of your test to a temporary store.
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A `PSDrive` is available for file activity during a tests and this drive is limited to the scope of a single `Describe` block. The contents of the drive are cleared when a `Context` block is exited.
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A test may need to work with file operations and validate certain types of file activities. It is usually desirable not to perform file activity tests that will produce side effects outside of an individual test. Pester creates a `PSDrive` inside the user's temporary drive that is accessible via `TestDrive:` or `$TestDrive`. Pester will remove this drive after the test completes. You may use this drive to isolate the file operations of your test to a temporary store.
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The following example illustrates the feature:
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@ -130,7 +139,7 @@ Describe "Add-Footer" {
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}
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```
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When this test completes, the contents of the TestDrive PSDrive will be removed.
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When this test completes, the contents of the `TestDrive:` `PSDrive` will be removed.
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#### Parameter Generation
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@ -145,7 +154,7 @@ $testCases = @(
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Describe "A test" {
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It "<a> -xor <b> should be <expectedresult>" -testcase $testcases {
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param ($a, $b, $ExpectedResult)
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$a -xor $b | Should Be $ExpectedResult
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$a -xor $b | Should -Be $ExpectedResult
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}
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}
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```
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@ -153,20 +162,23 @@ Describe "A test" {
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You can also construct loops and pass values as parameters, including the expected value, but Pester does this for you.
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#### Mocking
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Mocks the behavior of an existing command with an alternate implementation. This creates new behavior for any existing command within the scope of a Describe or Context block. The function allows you to specify a script block that will become the command's new behavior.
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Mocks the behavior of an existing command with an alternate implementation. This creates new behavior for any existing command within the scope of a `Describe` or `Context` block. The function allows you to specify a script block that will become the command's new behavior.
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The following example illustrates simple use:
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```powershell
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Context "Get-Random is not random" {
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Mock Get-Random { return 3 }
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It "Get-Random returns 3" {
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Get-Random | Should Be 3
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Get-Random | Should -Be 3
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}
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}
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```
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More information may be found on the [wiki](https://github.com/pester/Pester/wiki/Mock)
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### Free Code in a Describe block
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Code execution in Pester can be very subtle and can cause issues when executing test code. The execution of code which lays outside of the usual code blocks may not happen as you expect. Consider the following:
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```powershell
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@ -186,7 +198,7 @@ Describe it {
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Write-Host -for DarkRed "Before It"
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It "should not be a surprise" {
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1 | should be 1
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1 | should -Be 1
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}
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Write-Host -for DarkRed "After It"
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}
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@ -197,7 +209,7 @@ Describe it {
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}
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```
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Now, when run, you can see the execution schedule
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Now, when run, you can see the execution schedule:
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```
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PS# invoke-pester c:\temp\pester.demo.tests.ps1
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@ -223,10 +235,13 @@ Tests completed in 79ms
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Passed: 1 Failed: 0 Skipped: 0 Pending: 0
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```
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The DESCRIBE BeforeAll block is executed before any other code even though it was at the bottom of the Describe block, so if state is set elsewhere in the describe BLOCK, that state will not be visible (as the code will not yet been run). Notice, too, that the BEFOREALL block in Context is executed before any other code in that block.
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Generally, you should have code reside in one of the code block elements of `[Before|After][All|Each]`, especially if those block rely on state set by free code elsewhere in the block.
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The `Describe` `BeforeAll` block is executed before any other code even though it was at the bottom of the `Describe` block,
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so if state is set elsewhere in the `Describe` block, that state will not be visible (as the code will not yet been run). Notice, too,
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that the `BeforeAll` block in `Context` is executed before any other code in that block.
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Generally, you should have code reside in one of the code block elements of `[Before|After][All|Each]`, especially if those blocks rely on state set by free code elsewhere in the block.
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#### Skipping tests in bulk
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Sometimes it is beneficial to skip all the tests in a particular `Describe` block. For example, tests which are not applicable to a platform could be skipped, and they would be reported as skipped. The following is an example of how this may be done:
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```powershell
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Describe "Should not run these tests on non-Windows platforms" {
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@ -241,18 +256,18 @@ Describe "Should not run these tests on non-Windows platforms" {
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}
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Context "Block 1" {
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It "This block 1 test 1" {
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1 | should be 1
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1 | should -Be 1
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}
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It "This is block 1 test 2" {
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1 | should be 1
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1 | should -Be 1
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}
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}
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Context "Block 2" {
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It "This block 2 test 1" {
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2 | should be 1
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2 | should -Be 1
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}
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It "This is block 2 test 2" {
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2 | should be 1
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2 | should -Be 1
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}
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}
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}
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@ -277,25 +292,24 @@ Describing Should not run these tests on non-Windows platforms
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[-] This block 2 test 1 52ms
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Expected: {1}
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But was: {2}
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22: 2 | should be 1
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22: 2 | should -Be 1
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at <ScriptBlock>, <No file>: line 22
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[-] This is block 2 test 2 77ms
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Expected: {1}
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But was: {2}
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25: 2 | should be 1
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25: 2 | should -Be 1
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at <ScriptBlock>, <No file>: line 25
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```
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this technique uses the `$PSDefaultParameterValues` feature of PowerShell to temporarily set the It block parameter `-skip` to true (or in the case of Windows, it is not set at all)
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#### Multi-line strings
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You may want to have a test like
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```powershell
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It 'tests multi-line string' {
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Get-MultiLineString | Should Be @'
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Get-MultiLineString | Should -Be @'
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first line
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second line
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'@
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@ -307,10 +321,10 @@ The reason for it are line-ends.
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They cause problems for two reasons:
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* They are different on different platforms (`\r\n` on windows and `\n` on unix).
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* They are different on different platforms (`\r\n` on Windows and `\n` on Unix).
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* Even on the same system, they depends on the way how the repo was cloned.
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Particularly, in the default AppVeyour CI windows image, you will get `\n` line ends in all your files.
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Particularly, in the default AppVeyor CI Windows image, you will get `\n` line ends in all your files.
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That causes problems, because at runtime `Get-MultiLineString` would likely produce `\r\n` line ends on windows.
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Some workaround could be added, but they are sub-optimal and make reading test code harder.
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@ -322,7 +336,7 @@ function normalizeEnds([string]$text)
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}
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It 'tests multi-line string' {
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normalizeEnds (Get-MultiLineString) | Should Be (normalizeEnds @'
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normalizeEnds (Get-MultiLineString) | Should -Be (normalizeEnds @'
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first line
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second line
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'@)
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@ -339,11 +353,12 @@ Pester Do and Don't
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===================
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## Do
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1. Name your files <descriptivetest>.tests.ps1
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2. Keep tests simple
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1. Test only what you need
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2. Reduce dependencies
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3. Be sure to tag your `Describe` blocks based on their purpose
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1. Name your files `<descriptivetest>.tests.ps1`.
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2. Keep tests simple:
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1. Test only what you need.
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2. Reduce dependencies.
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3. Be sure to tag your `Describe` blocks based on their purpose:
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1. Tag `CI` indicates that it will be run as part of the continuous integration process. These should be unit test like, and generally take less than a second.
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2. Tag `Feature` indicates a higher level feature test (we will run these on a regular basis), for example, tests which go to remote resources, or test broader functionality
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3. Tag `Scenario` indicates tests of integration with other features (these will be run on a less regular basis and test even broader functionality than feature tests.
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@ -352,14 +367,14 @@ Pester Do and Don't
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5. Use `Context` to group tests
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1. Multiple `Context` blocks can help you group your test suite into logical sections
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6. Use `BeforeAll`/`AfterAll`/`BeforeEach`/`AfterEach` instead of custom initiators
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7. Prefer Try-Catch for expected errors and check $_.fullyQualifiedErrorId (don't use `should throw`)
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7. Prefer Try-Catch for expected errors and check `$_.fullyQualifiedErrorId` (don't use `should throw`).
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8. Use `-testcases` when iterating over multiple `It` blocks
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9. Use code coverage functionality where appropriate
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10. Use `Mock` functionality when you don't have your entire environment
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11. Avoid free code in a `Describe` block
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1. Use `[Before|After][Each|All]` see [Free Code in a Describe block](WritingPesterTests.md#free-code-in-a-describe-block)
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12. Avoid creating or using test files outside of TESTDRIVE:
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1. TESTDRIVE: has automatic clean-up
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12. Avoid creating or using test files outside of `TESTDRIVE:`
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1. `TESTDRIVE:` has automatic clean-up
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13. Keep in mind that we are creating cross platform tests
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1. Avoid using the registry
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2. Avoid using COM
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@ -367,8 +382,9 @@ Pester Do and Don't
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1. ex: checking for the count of loaded format files, check rather for format data for a specific type
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## Don't
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1. Don't have too many evaluations in a single It block
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1. Don't have too many evaluations in a single `It` block
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1. The first `Should` failure will stop that block
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2. Don't use `Should` outside of an `It` Block
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3. Don't use the word "Error" or "Fail" to test a positive case
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1. ex: "Get-ChildItem TESTDRIVE: shouldn't fail", rather "Get-ChildItem should be able to retrieve file listing from TESTDRIVE"
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1. ex: `"Get-ChildItem TESTDRIVE: shouldn't fail"`, rather than `"Get-ChildItem should be able to retrieve file listing from TESTDRIVE"`.
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