diff --git a/appveyor.yml b/appveyor.yml
index d1f3a05..db82d20 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -20,7 +20,7 @@ image: Visual Studio 2017
 
 install:
   - ps: Import-Module .\tools\AppVeyor.psm1
-  - ps: Invoke-InstallDependencies -Verbose
+  - ps: Invoke-InstallDependencies
 
 environment:
   NuGetToken:
diff --git a/src/Helper/Get-RandomKey.ps1 b/src/Helper/Get-RandomKey.ps1
index 206f400..907160a 100644
--- a/src/Helper/Get-RandomKey.ps1
+++ b/src/Helper/Get-RandomKey.ps1
@@ -32,6 +32,7 @@ function Get-RandomKey {
     [CmdletBinding()]
     param(
         [Parameter(Mandatory = $true)]
+        [ValidateNotNullOrEmpty()]
         [ValidateSet(16, 24, 32)]
         [string]$size
     )
diff --git a/src/Helper/Test-Module.ps1 b/src/Helper/Test-Module.ps1
index 75d7720..f116459 100644
--- a/src/Helper/Test-Module.ps1
+++ b/src/Helper/Test-Module.ps1
@@ -83,14 +83,14 @@ Could not find the required {0} called {1}. Please install the required {0} to r
             }
 
             'PSSnapin' {
-                if (Get-PSSnapin -Name $Name -Registered) {
+                if (Get-PSSnapin -Name $Name -Registered -ErrorAction SilentlyContinue) {
                     return $true
                 }
                 else {
                     if ($StopIfFails) {
                         Write-Error -Message $Message -ErrorAction Stop -Category NotInstalled
-                        return $false
                     }
+                    return $false
                 }
             }
 
diff --git a/tests/ChallengeFile/01_Set-ChallengeFile.Tests.ps1 b/tests/ChallengeFile/01_Set-ChallengeFile.Tests.ps1
new file mode 100644
index 0000000..0a68473
--- /dev/null
+++ b/tests/ChallengeFile/01_Set-ChallengeFile.Tests.ps1
@@ -0,0 +1,60 @@
+#region HEADER
+$RepoRoot = (Get-GitDirectory).replace('\.git', '')
+$sut = (Split-Path -Leaf $MyInvocation.MyCommand.Path) -replace '\.Tests\.', '.'
+$sut = $sut -replace "\d{2}`_", ''
+$suthome = (Get-ChildItem -Path $RepoRoot -Exclude ".\tests\" -Filter $sut -Recurse).FullName
+# Skip try loading the source file if it doesn't exists.
+If ($suthome.Length -gt 0) {
+    . $suthome
+}
+Else {
+    Write-Warning ("Could not find source file {0}" -f $sut)
+}
+
+# load additional functions defined in the repository. Replace the expression <FunctionName>.
+. (Get-ChildItem -Path $RepoRoot -Filter "Get-RandomKey.ps1" -Recurse).FullName
+
+#endregion HEADER
+
+Describe "Set-ChallengeFile" {
+    Context "Tests with custom path" {
+        It "Working dir and path not exist" {
+            {Set-ChallengeFile -Path 'C:\PSCredentialStore\Challenge.bin'} | Should -Not -Throw
+        }
+        It "No parameter and non file should return true" {
+            if (Test-Path -Path ("{0}\PSCredentialStore\Challenge.bin" -f $env:ProgramData)) {
+                Remove-Item -Path ("{0}\PSCredentialStore\Challenge.bin" -f $env:ProgramData)
+            }
+            Set-ChallengeFile
+            Test-Path -Path ("{0}\PSCredentialStore\Challenge.bin" -f $env:ProgramData) | Should -Be $true
+        }
+        It "Existing Credential file should return error" {
+            { Set-ChallengeFile } | Should -Throw
+            Remove-Item -Path ("{0}\PSCredentialStore\Challenge.bin" -f $env:ProgramData)
+        }
+        It "Use -Force switch should create a new challenge file" {
+            # prepare for test and clean up old data
+            if (Test-Path -Path ("{0}\PSCredentialStore\Challenge.bin" -f $env:ProgramData)) {
+                Remove-Item -Path ("{0}\PSCredentialStore\Challenge.bin" -f $env:ProgramData)
+            }
+            Set-ChallengeFile
+            { Set-ChallengeFile -Force } | Should -Not -Throw
+        }
+        It "Test directory creation for shared store" {
+            if (Test-Path -Path ("{0}\PSCredentialStore" -f $env:ProgramData)) {
+                Remove-Item -Path ("{0}\PSCredentialStore" -f $env:ProgramData) -Force -Recurse
+            }
+            Set-ChallengeFile
+            Test-Path -Path ("{0}\PSCredentialStore" -f $env:ProgramData) | Should -Be $true
+        }
+    }
+    Context "General Exception handling" {
+        Mock New-Item {throw "foobar exception"}
+        It "Test exception handling if the root directory could not be created" {
+            if (Test-Path -Path ("{0}\PSCredentialStore" -f $env:ProgramData)) {
+                Remove-Item -Path ("{0}\PSCredentialStore" -f $env:ProgramData) -Force -Recurse
+            }
+            { Set-ChallengeFile } | Should -Throw "Could not create the parent data dir"
+        }
+    }
+}
diff --git a/tests/ChallengeFile/01_Test-ChallengeFile.Tests.ps1 b/tests/ChallengeFile/01_Test-ChallengeFile.Tests.ps1
new file mode 100644
index 0000000..285fddc
--- /dev/null
+++ b/tests/ChallengeFile/01_Test-ChallengeFile.Tests.ps1
@@ -0,0 +1,38 @@
+#region HEADER
+$RepoRoot = (Get-GitDirectory).replace('\.git', '')
+$sut = (Split-Path -Leaf $MyInvocation.MyCommand.Path) -replace '\.Tests\.', '.'
+$sut = $sut -replace "\d{2}`_", ''
+$suthome = (Get-ChildItem -Path $RepoRoot -Exclude ".\tests\" -Filter $sut -Recurse).FullName
+# Skip try loading the source file if it doesn't exists.
+If ($suthome.Length -gt 0) {
+    . $suthome
+}
+Else {
+    Write-Warning ("Could not find source file {0}" -f $sut)
+}
+
+# load additional functions defined in the repository. Replace the expression <FunctionName>.
+#. (Get-ChildItem -Path $RepoRoot -Filter "Test-ChallengeFile.ps1" -Recurse).FullName
+
+#endregion HEADER
+
+Describe "Test-ChallengeFile" {
+    Context "Basic input tests" {
+        Mock Test-Path {return $true}
+        It "No parameter with existing challenge file" {
+            {Test-ChallengeFile} | Should -Not -Throw
+        }
+        It "No parameter and existing file should return true" {
+            Test-ChallengeFile | Should -Be $true
+        }
+    }
+    Context "Execute with parameter" {
+        $TestChFile = "{0}\resources\cs\Challenge.bin" -f $RepoRoot
+        It "Provide valid path" {
+            Test-ChallengeFile -Path $TestChFile | Should -Be $true
+        }
+        It "Provide fake path" {
+            Test-ChallengeFile -Path "C:\notexisting.bin" | Should -Be $false
+        }
+    }
+}
diff --git a/tests/Helper/01_Get-ModuleBase.Tests.ps1 b/tests/Helper/01_Get-ModuleBase.Tests.ps1
new file mode 100644
index 0000000..55ba4f6
--- /dev/null
+++ b/tests/Helper/01_Get-ModuleBase.Tests.ps1
@@ -0,0 +1,25 @@
+#region HEADER
+$RepoRoot = (Get-GitDirectory).replace('\.git', '')
+$sut = (Split-Path -Leaf $MyInvocation.MyCommand.Path) -replace '\.Tests\.', '.'
+$sut = $sut -replace "\d{2}`_", ''
+$suthome = (Get-ChildItem -Path $RepoRoot -Exclude ".\tests\" -Filter $sut -Recurse).FullName
+# Skip try loading the source file if it doesn't exists.
+If ($suthome.Length -gt 0) {
+    . $suthome
+}
+Else {
+    Write-Warning ("Could not find source file {0}" -f $sut)
+}
+
+# load additional functions defined in the repository. Replace the expression <FunctionName>.
+# . (Get-ChildItem -Path $RepoRoot -Filter "<FunctionName>.ps1" -Recurse).FullName
+
+#endregion HEADER
+
+Describe "Get-ModuleBase" {
+    Context "Basic syntax check" {
+        It "Test1: Should not throw" {
+            { Get-ModuleBase } | Should -Not -Throw
+        }
+    }
+}
diff --git a/tests/Helper/01_Get-RandomKey.Tests.ps1 b/tests/Helper/01_Get-RandomKey.Tests.ps1
new file mode 100644
index 0000000..f6ab645
--- /dev/null
+++ b/tests/Helper/01_Get-RandomKey.Tests.ps1
@@ -0,0 +1,39 @@
+#region HEADER
+$RepoRoot = (Get-GitDirectory).replace('\.git', '')
+$sut = (Split-Path -Leaf $MyInvocation.MyCommand.Path) -replace '\.Tests\.', '.'
+$sut = $sut -replace "\d{2}`_", ''
+$suthome = (Get-ChildItem -Path $RepoRoot -Exclude ".\tests\" -Filter $sut -Recurse).FullName
+# Skip try loading the source file if it doesn't exists.
+If ($suthome.Length -gt 0) {
+    . $suthome
+}
+Else {
+    Write-Warning ("Could not find source file {0}" -f $sut)
+}
+
+# load additional functions defined in the repository. Replace the expression <FunctionName>.
+# . (Get-ChildItem -Path $RepoRoot -Filter "<FunctionName>.ps1" -Recurse).FullName
+
+#endregion HEADER
+
+Describe "Get-RandomKey" {
+    Context "Basic input tests" {
+        It "Test1: Should throw if wrong size is given" {
+            {Get-RandomKey -size 43} | Should -Throw
+        }
+    }
+    Context "Basic syntax check" {
+        It "Test1: Should return a key with a length of 16" {
+            $Key = Get-RandomKey -size 16
+            $Key.length | Should -Be 16
+        }
+        It "Test2: Should return a key with a length of 24" {
+            $Key = Get-RandomKey -size 24
+            $Key.length | Should -Be 24
+        }
+        It "Test3: Should return a key with a length of 32" {
+            $Key = Get-RandomKey -size 32
+            $Key.length | Should -Be 32
+        }
+    }
+}
diff --git a/tests/Helper/01_Test-Module.Tests.ps1 b/tests/Helper/01_Test-Module.Tests.ps1
new file mode 100644
index 0000000..675a2dc
--- /dev/null
+++ b/tests/Helper/01_Test-Module.Tests.ps1
@@ -0,0 +1,65 @@
+#region HEADER
+$RepoRoot = (Get-GitDirectory).replace('\.git', '')
+$sut = (Split-Path -Leaf $MyInvocation.MyCommand.Path) -replace '\.Tests\.', '.'
+$sut = $sut -replace "\d{2}`_", ''
+$suthome = (Get-ChildItem -Path $RepoRoot -Exclude ".\tests\" -Filter $sut -Recurse).FullName
+# Skip try loading the source file if it doesn't exists.
+If ($suthome.Length -gt 0) {
+    . $suthome
+}
+Else {
+    Write-Warning ("Could not find source file {0}" -f $sut)
+}
+
+# load additional functions defined in the repository. Replace the expression <FunctionName>.
+#. (Get-ChildItem -Path $RepoRoot -Filter "<FunctionName>.ps1" -Recurse).FullName
+
+#endregion HEADER
+
+Describe "Test-ModuleName" {
+    Context "Basic input tests" {
+        It "Testing standard module should not throw" {
+            { Test-Module -Name 'PowerShellGet' -Type Module } | Should -Not -Throw
+        }
+        It "Existing module should return true" {
+            Test-Module -Name 'PowerShellGet' -Type Module | Should -Be $true
+        }
+    }
+    Context "Custom Type tests" {
+        It "Using custom type should throw" {
+            { Test-Module -Name "foobarr" -Type Custom} | Should -Throw
+        }
+    }
+    Context "Working with PSSnapins" {
+        It "Loading first PSSnaping should not throw " {
+            $Snap = Get-PSSnapin -Registered | Select-Object -First 1
+            { Test-Module -Name $Snap.Name -Type PSSnapin } | Should -Not -Throw
+        }
+        It "Loading first PSSnaping should return true" {
+            $Snap = Get-PSSnapin -Registered | Select-Object -First 1
+            Test-Module -Name $Snap.Name -Type PSSnapin | Should -Be $true
+        }
+        It "Not existing PSSnaping should return false" {
+            Test-Module -Name 'foobar2000' -Type PSSnapin | Should -Be $false
+        }
+        It "StopifFails switch should thrown an error" {
+            {Test-Module -Name 'foobar2000' -Type PSSnapin -StopIfFails }| Should -Throw
+        }
+    }
+    Context "Working with modules" {
+        It "Loading first module should not throw " {
+            $Mod = Get-Module -ListAvailable | Select-Object -First 1
+            { Test-Module -Name $Mod.Name -Type Module } | Should -Not -Throw
+        }
+        It "Loading first module should return true" {
+            $Snap = Get-Module -ListAvailable | Select-Object -First 1
+            Test-Module -Name $Snap.Name -Type Module | Should -Be $true
+        }
+        It "Not existing module should return false" {
+            Test-Module -Name 'foobar2000' -Type Module | Should -Be $false
+        }
+        It "StopifFails switch should thrown an error" {
+            {Test-Module -Name 'foobar2000' -Type Module -StopIfFails }| Should -Throw
+        }
+    }
+}
diff --git a/tests/Item/02_New-CredentialStoreItem.Tests.ps1 b/tests/Item/02_New-CredentialStoreItem.Tests.ps1
index f1914bb..6b711ef 100644
--- a/tests/Item/02_New-CredentialStoreItem.Tests.ps1
+++ b/tests/Item/02_New-CredentialStoreItem.Tests.ps1
@@ -61,5 +61,42 @@ Describe "New-CredentialStoreItem" {
             $res = Get-Member -InputObject $tmpCS -Name $RemoteHost -Membertype Properties
             $res.Name | Should Be $RemoteHost
         }
+        It "Adds Item with identifier to shared store" {
+            $tmpCS = 'C:\CredentialStore.json'
+            $UserName = "myuser"
+            $Password = ConvertTo-SecureString -String "mypasswd" -AsPlainText -Force
+            $mycreds = New-Object -TypeName PSCredential -ArgumentList $UserName, $Password
+            $RemoteHost = "foobar2"
+            New-CredentialStoreItem -Path $tmpCS -RemoteHost $RemoteHost -Credential $mycreds -Identifier 'Foo'
+            $writtenItem = Get-CredentialStoreItem -Path $tmpCS -RemoteHost $RemoteHost -Identifier 'Foo'
+            ($writtenItem.UserName -eq $UserName) -and ($writtenItem.Password.Length -gt 0) | Should -Be $true
+        }
     }
+    Context "Test optional parameter lookup" {
+        Mock Get-Credential {
+            $UserName = 'testuser'
+            $Password = ConvertTo-SecureString -String "mypasswd" -AsPlainText -Force
+            return [PSCredential]::new($UserName, $Password)
+
+        }
+        It "Test missing Credential" {
+            $tmpCS = 'C:\CredentialStore.json'
+            New-CredentialStoreItem -Path $tmpCs -Shared -RemoteHost 'foobar3'
+            $writtenItem = Get-CredentialStoreItem -Path $tmpCS -Shared -RemoteHost 'foobar3'
+            $writtenItem.UserName | Should -Be "testuser"
+        }
+    }
+    Context "General Exception handling" {
+        Mock Test-CredentialStore {return $false}
+        Mock Get-Credential {
+            $UserName = 'myUser'
+            $Password = ConvertTo-SecureString -String "mypasswd" -AsPlainText -Force
+            return [PSCredential]::new($UserName, $Password)
+
+        }
+        It "Missing CredentialStore should throw" {
+            { New-CredentialStoreItem -Path 'C:\missingStore.json' -RemoteHost 'notrelevant' } | Should -Throw "Could not add anything"
+        }
+    }
+
 }
diff --git a/tests/Store/01_Get-CredentialStore.Tests.ps1 b/tests/Store/01_Get-CredentialStore.Tests.ps1
index a0cab26..e52f147 100644
--- a/tests/Store/01_Get-CredentialStore.Tests.ps1
+++ b/tests/Store/01_Get-CredentialStore.Tests.ps1
@@ -33,5 +33,15 @@ Describe "Get-CredentialStore" {
 
             {Get-CredentialStore -Path $TestCredentialStore} | Should Not Throw
         }
+        It "Test3: Not existing path should return false" {
+            { Get-CredentialStore -Path 'C:\foobar\CredentialStore.json' -Shared }| Should -Throw "Could not find the CredentialStore."
+        }
+    }
+    Context "Testing invalid json data" {
+        Mock Test-CredentialStore {return $true}
+        Mock Get-Content {return '"foo":"bar",'}
+        It "Should throw with invalid CredentialStore" {
+            { Get-Credentialstore -Path "C:\dummy.json"} | Should -Throw "Unknown CredentialStore format. Invalid JSON file."
+        }
     }
 }
diff --git a/tests/Store/01_New-CredentialStore.Tests.ps1 b/tests/Store/01_New-CredentialStore.Tests.ps1
index dfc47b0..b9d2eee 100644
--- a/tests/Store/01_New-CredentialStore.Tests.ps1
+++ b/tests/Store/01_New-CredentialStore.Tests.ps1
@@ -92,6 +92,12 @@ Describe "New-CredentialStore" {
             {New-CredentialStore -Path $pCS -Shared -Force} | Should Not Throw
         }
     }
+    Context "Test exception handling" {
+        Mock Out-File {throw "foobar exception"}
+        It "JSON Converstion should fail and throw" {
+            { New-CredentialStore -Path "C:\dummy.json"} | Should -Throw
+        }
+    }
 }
 
 # Cleanup test stores and restore existing ones.
diff --git a/tests/Store/01_Test-CredentialStore.Tests.ps1 b/tests/Store/01_Test-CredentialStore.Tests.ps1
index 693184f..b32738f 100644
--- a/tests/Store/01_Test-CredentialStore.Tests.ps1
+++ b/tests/Store/01_Test-CredentialStore.Tests.ps1
@@ -36,5 +36,14 @@ Describe "Test-CredentialStore" {
             $res | Should Be $False
             $WarningPreference = $oWarningPreference
         }
+        It "Test4: Not existing path should return false" {
+            Test-CredentialStore -Path 'C:\foobar\CredentialStore.json' | Should -Be $false
+        }
+        It "Test5: testing private CredentialStore path" {
+            if (Test-Path -Path ("{0}\CredentialStore.json" -f $env:APPDATA) ) {
+                Remove-Item -Path ("{0}\CredentialStore.json" -f $env:APPDATA)
+            }
+            Test-CredentialStore | Should -Be $false
+        }
     }
 }
diff --git a/tools/AppVeyor.psm1 b/tools/AppVeyor.psm1
index 71e1e85..ac35426 100644
--- a/tools/AppVeyor.psm1
+++ b/tools/AppVeyor.psm1
@@ -154,7 +154,6 @@ Function Invoke-CoverageReport() {
         [String]$RepoToken = $Env:CoverallsToken
     )
 
-    Import-Module ('.\src\{0}.psm1' -f $CALLSIGN) -Verbose -Force
     $FileMap = New-PesterFileMap -SourceRoot '.\src' -PesterRoot '.\tests'
     $CoverageReport = New-CoverageReport -PesterFileMap $FileMap -RepoToken $RepoToken
     Write-Host "CoverageReport JSON:" -ForegroundColor Yellow