Replace escape characters in Format-String2

src/Format2.ps1

@@ -1,4 +1,8 @@
-function Format-Collection2 ($Value, [switch]$Pretty) {
+
+# 0x1B is escape, the control code "`e" was introduces in Powershell 7, and so we write it directly as the number here.
+[char[]] $script:specialChars = foreach ($ch in ("`0", "`a", "`b", "`t", "`f", "`r", "`n", 0x1B)) { [char]$ch }
+
+function Format-Collection2 ($Value, [switch]$Pretty) {
     $length = 0
     $o = foreach ($v in $Value) {
         $formatted = Format-Nicely2 -Value $v -Pretty:$Pretty
@@ -45,11 +49,35 @@ function Format-Object2 ($Value, $Property, [switch]$Pretty) {
     $o
 }
 
+function Replace-SpecialCharactersInString ($Value) {
+
+}
 function Format-String2 ($Value) {
     if ('' -eq $Value) {
         return '<empty>'
     }
 
+
+    # Special characters like `n or `e should be rendered as their visible versions.
+    # Especially `e which is used in ANSI codes and can entirely break our output.
+    #
+    # We convert each of these using the unicode printable version,
+    # which is obtained by adding 0x2400
+    [int]$unicodeControlPictures = 0x2400
+
+    if (0 -lt $Value.IndexOfAny($script:specialChars)) {
+        $chars = [char[]]$Value
+        $charCount = $chars.Length
+        for ($j = 0; $j -lt $charCount; $j++) {
+            $char = $chars[$j]
+            if ($char -in $script:specialChars) {
+                $chars[$j] = [char]([int]$char + $unicodeControlPictures)
+            }
+        }
+
+        $Value = $chars -join ''
+    }
+
     "'$Value'"
 }
 

src/functions/TestResults.NUnit3.ps1

@@ -1,6 +1,6 @@
 # NUnit3 schema docs: https://docs.nunit.org/articles/nunit/technical-notes/usage/Test-Result-XML-Format.html
 
-[char[]] $script:invalidCDataChars = foreach ($ch in (0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x0B, 0x0C, 0x0E, 0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F)) { [char]$ch }
+[char[]] $script:invalidCDataChars = foreach ($ch in (0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x0B, 0x0C, 0x0E, 0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F)) { [char]$ch }
 
 function Write-NUnit3Report([Pester.Run] $Result, [System.Xml.XmlWriter] $XmlWriter) {
     # Write the XML Declaration

tst/Format2.Tests.ps1

@@ -209,8 +209,41 @@ InPesterModuleScope {
             Format-String2 -Value "" | Verify-Equal '<empty>'
         }
 
-        It "Formats string to be sorrounded by quotes" {
+        It "Formats string to be surrounded by quotes" {
             Format-String2 -Value "abc" | Verify-Equal "'abc'"
         }
+
+
+        It "Replaces ansi escapes with their showable equivalent" -ForEach @(
+            @{ Value = "`0"; Expected = '␀'; PowerShellVersion = 5 }
+            @{ Value = "`a"; Expected = '␇'; PowerShellVersion = 5 }
+            @{ Value = "`b"; Expected = '␈'; PowerShellVersion = 5 }
+            @{ Value = "`t"; Expected = '␉'; PowerShellVersion = 5 }
+            @{ Value = "`f"; Expected = '␌'; PowerShellVersion = 5 }
+            @{ Value = "`r"; Expected = '␍'; PowerShellVersion = 5 }
+            @{ Value = "`n"; Expected = '␊'; PowerShellVersion = 5 }
+            # Escape for escape was introduced in PowerShell 7
+            @{ Value = "`e"; Expected = '␛'; PowerShellVersion = 7 }
+        ) {
+            if ($PSVersionTable.PSVersion.Major -lt $PowerShellVersion) {
+                continue
+            }
+
+            Format-String2 -Value "-$value-" | Verify-Equal "'-$expected-'"
+        }
+
+        It "Does not replace non escaped values with escapes" -ForEach @(
+            @{ Value = "0"; Expected = '0' }
+            @{ Value = "a"; Expected = 'a' }
+            @{ Value = "b"; Expected = 'b' }
+            @{ Value = "t"; Expected = 't' }
+            @{ Value = "f"; Expected = 'f' }
+            @{ Value = "r"; Expected = 'r' }
+            @{ Value = "n"; Expected = 'n' }
+            @{ Value = "e"; Expected = 'e' }
+        ) {
+            Format-String2 -Value "-$value-" | Verify-Equal "'-$expected-'"
+        }
+
     }
 }

tst/functions/assert/String/Should-BeString.Tests.ps1

@@ -120,4 +120,9 @@ Describe "Should-BeString" {
         $err = { Should-BeString -Expected "abc" -Actual "bde" } | Verify-AssertionFailed
         $err.Exception.Message | Verify-Equal "Expected [string] 'abc', but got [string] 'bde'."
     }
+
+    It "Handles escape character in the error message" {
+        $err = { Should-BeString -Expected "ee `e ee" -Actual "mmmmm" } | Verify-AssertionFailed
+        $err.Exception.Message | Verify-Equal "Expected [string] 'ee ␛ ee', but got [string] 'mmmmm'."
+    }
 }