diff --git a/tests/Public/Add-WorkingDays.Tests.ps1 b/tests/Public/Add-WorkingDays.Tests.ps1
new file mode 100644
index 0000000..b6d67c1
--- /dev/null
+++ b/tests/Public/Add-WorkingDays.Tests.ps1
@@ -0,0 +1,29 @@
+BeforeAll {
+    # Always use built code if running in a pipeline
+    if ($env:USER -eq 'runner') {
+        Import-Module "$PSScriptRoot/../../build/PSBusinessTime/PSBusinessTime.psd1" -Force
+    }
+    # Check if module is already imported, as it can be via VSCode task where you can choose what code base to test
+    # and you might not want to cloober it with the non-built code
+    elseif (-not (Get-Module PSBusinessTime)) {
+        Import-Module "$PSScriptRoot/../../src/PSBusinessTime.psd1" -Force
+    }
+}
+
+Describe "Add-WorkingDays" {
+    It "should be 2022-04-19 as 3 working days from 2022-04-14" {
+        Add-WorkingDays -Date (Get-Date '2022-04-14') -Days 3 | Should -Be (Get-Date '2022-04-19')
+    }
+
+    It "should be 2022-04-11 as -3 working days from 2022-04-14" {
+        Add-WorkingDays -Date (Get-Date '2022-04-14') -Days -3 | Should -Be (Get-Date '2022-04-11')
+    }
+
+    It "should be 2022-04-21 as 3 working days from 2022-04-14, with Good Friday and Easter Monday holidays" {
+        Add-WorkingDays -Date (Get-Date '2022-04-14') -Days 3 -NonWorkingDates (Get-Date '2022-04-15'),(Get-Date '2022-04-18') | Should -Be (Get-Date '2022-04-21')
+    }
+
+    It "should be 2022-04-21 as 3 working days from 2022-04-14, excluding Friday, Saturday, Sunday, and Monday, as working days" {
+        Add-WorkingDays -Date (Get-Date '2022-04-14') -Days 3 -NonWorkingDaysOfWeek 'Friday','Saturday','Sunday','Monday' | Should -Be (Get-Date '2022-04-21')
+    }
+}
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