Comparing double and single values (floating point numbers) can lead to rounding errors. The way to get around this is to define a tolerance meaning just how much of a difference is acceptable when comparing two floating point numbers. To demonstrate how compare floating point values using PowerShell the PsUnit class will be extended to support an AreEqual method with the following signature:
class PsUnit {
hidden static [void] AreEqual(
[double] $leftValue,
[double] $rightValue,
[double] $tolerance,
[string] $filename,
[int] $lineNumber)
}
The PsUnit class was introduced in the post PowerShell: Unit Test Functions and Accessing the Invoking Code's Line Number. Recall from the aforementioned post that functions were used to wrap PsUnit methods in order to pass in the invoking code's filename and line number. The function to invoke the override of AreEqual that compares values of type double is AreEqualDouble:
function AreEqualDouble {
Param(
[double] $leftValue,
[double] $rightValue,
[double] $tolerance
)
[PsUnit]::AreEqual(
$leftValue,
$rightValue,
$tolerance,
$MyInvocation.ScriptName,
$MyInvocation.ScriptLineNumber)
}
The PsUnit class's methods that compares doubles or supports the comparing of doubles are defined as follows:
hidden static [void] AreEqualCoreValidations(
[object] $leftValue,
[object] $rightValue,
[string] $filename,
[int] $lineNumber) {
if (($null -eq $leftValue) -and ($null -eq $rightValue)) {
return
}
if ($null -eq $rightValue) {
throw [PsUnit]::CreateMessage(
"Test failed, assigned left value ($leftValue) cannot compared to right value of null",
$filename,
$lineNumber)
}
if ($null -eq $leftValue) {
throw [PsUnit]::CreateMessage(
"Test failed, assigned right value ($rightValue) cannot compared to left value of null",
$filename,
$lineNumber)
}
if ($leftValue.GetType() -ne $rightValue.GetType()) {
throw [PsUnit]::CreateMessage(
"Test failed type differ $($leftValue.GetType()) -ne $($rightValue.GetType())",
$filename,
$lineNumber)
}
}
hidden static [void] AreEqual(
[double] $leftValue,
[double] $rightValue,
[double] $tolerance,
[string] $filename,
[int] $lineNumber) {
[PsUnit]::AreEqualCoreValidations(
$leftValue,
$rightValue,
$filename,
$lineNumber)
if ([System.Math]::Abs($leftValue - $rightValue) -le
$tolerance) {
return
}
throw [PsUnit]::CreateMessage(
"Test failed: difference in values ($([System.Math]::Abs($leftValue - $rightValue))) exceeds tolerance ($tolerance)",
$filename,
$lineNumber)
}
The PsUnit class code, the wrapper functions, and the test functions are shown below in their entirety. All code related to the comparing of doubles is demarcated by boldface:
Set-StrictMode -Version 3.0
class PsUnit {
hidden static [string] $filenameLineNumberSeparator
hidden static [string] $filenameLineNumberStart
hidden static [string] $filenameLineNumberEnd
hidden static [string] $boolMismatchMessage
static PsUnit() {
[PsUnit]::filenameLineNumberStart = '('
[PsUnit]::filenameLineNumberEnd = ')'
[PsUnit]::filenameLineNumberSeparator = ':'
[PsUnit]::boolMismatchMessage = 'Test expected value of '
}
hidden static [string] CreateMessage(
[string] $message,
[string] $filename,
[int] $lineNumber) {
return "$message $([PsUnit]::filenameLineNumberStart)$filename" +
"$([PsUnit]::filenameLineNumberSeparator)$lineNumber$([PsUnit]::filenameLineNumberEnd)"
}
hidden static [void] IsTrue(
[bool] $shouldBeTrue,
[string] $filename,
[int] $lineNumber) {
if ($shouldBeTrue) {
return
}
throw [PsUnit]::CreateMessage(
"$([PsUnit]::boolMismatchMessage) $true",
$filename,
$lineNumber)
}
hidden static [void] IsFalse(
[bool] $shouldBeFalse,
[string] $filename,
[int] $lineNumber) {
if (!($shouldBeFalse)) {
return
}
throw [PsUnit]::CreateMessage(
"$([PsUnit]::boolMismatchMessage) $false",
$filename,
$lineNumber)
}
hidden static [void] AreEqualCoreValidations(
[object] $leftValue,
[object] $rightValue,
[string] $filename,
[int] $lineNumber) {
if (($null -eq $leftValue) -and ($null -eq $rightValue)) {
return
}
if ($null -eq $rightValue) {
throw [PsUnit]::CreateMessage(
"Test failed, assigned left value ($leftValue) cannot compared to right value of null",
$filename,
$lineNumber)
}
if ($null -eq $leftValue) {
throw [PsUnit]::CreateMessage(
"Test failed, assigned right value ($rightValue) cannot compared to left value of null",
$filename,
$lineNumber)
}
if ($leftValue.GetType() -ne $rightValue.GetType()) {
throw [PsUnit]::CreateMessage(
"Test failed type differ $($leftValue.GetType()) -ne $($rightValue.GetType())",
$filename,
$lineNumber)
}
}
hidden static [void] AreEqual(
[double] $leftValue,
[double] $rightValue,
[double] $tolerance,
[string] $filename,
[int] $lineNumber) {
[PsUnit]::AreEqualCoreValidations(
$leftValue,
$rightValue,
$filename,
$lineNumber)
if ([System.Math]::Abs($leftValue - $rightValue) -le $tolerance) {
return
}
throw [PsUnit]::CreateMessage(
"Test failed: difference in values ($([System.Math]::Abs($leftValue - $rightValue))) exceeds tolerance ($tolerance)",
$filename,
$lineNumber)
}
hidden static [void] AreEqual(
[object] $leftValue,
[object] $rightValue,
[string] $filename,
[int] $lineNumber) {
[PsUnit]::AreEqualCoreValidations(
$leftValue,
$rightValue,
$filename,
$lineNumber)
if ($leftValue -eq $rightValue) {
return
}
throw [PsUnit]::CreateMessage(
"Test failed: values not equal $leftValue -ne $rightValue",
$filename,
$lineNumber)
}
}
function IsTrue {
Param(
[Parameter(Mandatory=$true)]
[bool] $shouldBeTrue
)
[PsUnit]::IsTrue(
$shouldBeTrue,
$MyInvocation.ScriptName,
$MyInvocation.ScriptLineNumber)
}
function IsFalse {
Param(
[Parameter(Mandatory=$true)]
[bool] $shouldBeFalse
)
[PsUnit]::IsFalse(
$shouldBeFalse,
$MyInvocation.ScriptName,
$MyInvocation.ScriptLineNumber)
}
function AreEqual {
Param(
[object] $leftValue,
[object] $rightValue
)
[PsUnit]::AreEqual(
$leftValue,
$rightValue,
$MyInvocation.ScriptName,
$MyInvocation.ScriptLineNumber)
}
function AreEqualDouble {
Param(
[double] $leftValue,
[double] $rightValue,
[double] $tolerance
)
[PsUnit]::AreEqual(
$leftValue,
$rightValue,
$tolerance,
$MyInvocation.ScriptName,
$MyInvocation.ScriptLineNumber)
}
function Test-AreEqualUnequal {
Param(
[object] $leftValue,
[object] $rightValue
)
try {
AreEqual $leftValue $rightValue
}
catch {
return
}
throw "Exception should have been thrown ($($MyInvocation.ScriptName):$($MyInvocation.ScriptLineNumber))"
}
function Test-AreEqual {
try {
AreEqual $false $false
AreEqual $true $true
AreEqual $null $null
AreEqual 10 10
AreEqual 'xyZ' 'XYZ'
}
catch {
throw
}
Test-AreEqualUnequal 'xyZ' $null
Test-AreEqualUnequal $null 'xyZ'
Test-AreEqualUnequal 'qed' $null
Test-AreEqualUnequal $true $false
Test-AreEqualUnequal $false $true
Test-AreEqualUnequal 10 5
Test-AreEqualUnequal 'x' 5
}
function Test-AreEqualUnequalDouble {
Param(
[double] $leftValue,
[double] $rightValue,
[double] $tolerance
)
try {
AreEqualDouble $leftValue $rightValue $tolerance
}
catch {
return
}
throw "Exception should have been thrown ($($MyInvocation.ScriptName):$($MyInvocation.ScriptLineNumber))"
}
function Test-AreEqualDouble {
[double] $value01 = 0.1
[double] $value02 = 0.11
[double] $tolerance = 0.015
try {
AreEqualDouble $value01 $value02 $tolerance
$value02 = 0.09
AreEqualDouble $value01 $value02 $tolerance
$value01 = 100.0
$value02 = 110.0
$tolerance = 10.001
AreEqualDouble $value01 $value02 $tolerance
$value01 = -100.0
$value02 = -110.0
$tolerance = 10.001
AreEqualDouble $value01 $value02 $tolerance
$value01 = 0.01
$value02 = 0.01
$tolerance = 0
AreEqualDouble $value01 $value02 $tolerance
}
catch {
throw
}
$value01 = 100.0
$value02 = 110.0
$tolerance = 9.999
Test-AreEqualUnequal $value01 $value02 $tolerance
$value01 = -100.0
$value02 = -110.0
Test-AreEqualUnequal $value01 $value02 $tolerance
$value01 = 0.01
$value02 = 0.0101
$tolerance = 00009
Test-AreEqualUnequal $value01 $value02 $tolerance
Test-AreEqualUnequal $value01 $value02 $tolerance
$value01 = -0.01
$value02 = -0.0101
Test-AreEqualUnequal $value01 $value02 $tolerance
}
function Test-IsFalse {
[bool] $expectedException = $false
try {
IsFalse $false
IsFalse $($null -eq '')
$expectedException = $true
IsFalse $true
}
catch {
if ($expectedException) {
return
}
throw
}
}
function Test-IsTrue {
[bool] $expectedException = $false
try {
IsTrue $true
IsTrue $('AbC' -eq 'aBC')
$expectedException = $true
IsTrue $false
}
catch {
if ($expectedException) {
return
}
throw
}
}
try {
Test-AreEqual
Test-AreEqualDouble
Test-IsFalse
Test-IsTrue
Write-Host 'Success'
}
catch {
$errorRecord = $_
Write-Host "Error: $errorRecord.Exception"
Write-Host 'Failure'
}
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