test for IList per discussion in pester#785

self-limit recursion depth to cause fast(er) failure in case cyclic object graphs are encountered
alx9r · Aug 16, 2017 · e8268be · e8268be
1 parent 89340b8
commit e8268be
Show file tree

Hide file tree

Showing 2 changed files with 19 additions and 5 deletions.
diff --git a/Functions/Assertions/Be.Tests.ps1 b/Functions/Assertions/Be.Tests.ps1
@@ -85,11 +85,19 @@ InModuleScope Pester {
             {abc} | Should -CEQ "abc"
         }
 
-        It 'Does not overflow on IEnumerable' {
+        It 'Does not overflow on cyclic object graph' {
             # see https://github.com/pester/Pester/issues/785
             $doc = [xml]'<?xml version="1.0" encoding="UTF-8" standalone="no" ?><root></root>'
             $doc | Should be $doc
         }
+
+        Context 'recursion limit' {
+            Mock IsIList { $true }
+            It 'throws exception when self-imposed recursion limit is reached' {
+                $doc = [xml]''
+                { $doc | Should be $doc } | Should throw 'reached recursion depth limit'
+            }
+        }
     }
 
     Describe "PesterBeFailureMessage" {

diff --git a/Functions/Assertions/Be.ps1 b/Functions/Assertions/Be.ps1
@@ -178,8 +178,14 @@ function ArraysAreEqual
     param (
         [object[]] $First,
         [object[]] $Second,
-        [switch] $CaseSensitive
+        [switch] $CaseSensitive,
+        [int] $RecursionLimit = 100
     )
+    $recursionDepth++
+    if ( $recursionDepth -gt $RecursionLimit )
+    {
+        throw "reached recursion depth limit of $RecursionLimit when comparing arrays $First and $Second"
+    }
 
     # Do not remove the subexpression @() operators in the following two lines; doing so can cause a
     # silly error in PowerShell v3.  (Null Reference exception from the PowerShell engine in a
@@ -196,7 +202,7 @@ function ArraysAreEqual
 
     for ($i = 0; $i -lt $First.Count; $i++)
     {
-        if ((IsCollection $First[$i]) -or (IsCollection $Second[$i]))
+        if ((IsIList $First[$i]) -or (IsIList $Second[$i]))
         {
             if (-not (ArraysAreEqual -First $First[$i] -Second $Second[$i] -CaseSensitive:$CaseSensitive))
             {
@@ -231,11 +237,11 @@ function ArrayOrSingleElementIsNullOrEmpty
     return $null -eq $Array -or $Array.Count -eq 0 -or ($Array.Count -eq 1 -and $null -eq $Array[0])
 }
 
-function IsCollection
+function IsIList
 {
     param ([object] $InputObject)
 
-    return $InputObject -is [Array]
+    return [bool]$InputObject.GetType().GetInterface('IList')
 }
 
 function ReplaceValueInArray