test: add Pester tests for Initialize-PSBuild

tests/Initialize-PSBuild.tests.ps1

@@ -0,0 +1,57 @@
+Describe 'Initialize-PSBuild' {
+    BeforeAll {
+        Import-Module "$PSScriptRoot/../PowerShellBuild/PowerShellBuild.psd1" -Force
+    }
+
+    BeforeEach {
+        $script:capturedBuildOutput = $null
+        Mock -CommandName Set-BuildEnvironment -MockWith {
+            param($BuildOutput)
+            $script:capturedBuildOutput = $BuildOutput
+        }
+
+        $env:BHProjectPath = '/repo/project'
+        $env:BHProjectName = 'DemoModule'
+
+        $script:baseEnvironment = @{
+            Build = @{
+                OutDir = 'out'
+            }
+            General = @{
+                ModuleVersion = '1.2.3'
+            }
+        }
+    }
+
+    It 'sets ModuleOutDir under BHProjectPath when OutDir is relative' {
+        $envCopy = $script:baseEnvironment.PSObject.Copy()
+        Initialize-PSBuild -BuildEnvironment $script:baseEnvironment
+
+        $expected = [IO.Path]::Combine('/repo/project', 'out', 'DemoModule', '1.2.3')
+        $script:baseEnvironment.Build.ModuleOutDir | Should -Be $expected
+        $script:capturedBuildOutput | Should -Be $expected
+        Assert-MockCalled Set-BuildEnvironment -Times 1 -Exactly
+    }
+
+    It 'keeps OutDir-rooted path when OutDir already starts with BHProjectPath (case-insensitive)' {
+        $script:baseEnvironment.Build.OutDir = '/REPO/PROJECT/out'
+
+        Initialize-PSBuild -BuildEnvironment $script:baseEnvironment
+
+        $expected = [IO.Path]::Combine('/REPO/PROJECT/out', 'DemoModule', '1.2.3')
+        $script:baseEnvironment.Build.ModuleOutDir | Should -Be $expected
+        $script:capturedBuildOutput | Should -Be $expected
+        Assert-MockCalled Set-BuildEnvironment -Times 1 -Exactly
+    }
+
+    It 'prints BuildHelpers environment section only when UseBuildHelpers is present' {
+        Mock -CommandName Get-Item -MockWith { @() }
+        Mock -CommandName Write-Host
+
+        Initialize-PSBuild -BuildEnvironment $script:baseEnvironment
+        Assert-MockCalled Write-Host -Times 2 -Exactly
+
+        Initialize-PSBuild -BuildEnvironment $script:baseEnvironment -UseBuildHelpers
+        Assert-MockCalled Write-Host -Times 5
+    }
+}