Ensure NestedModules property gets populated by Test-ModuleManifest (#7859)

test/powershell/engine/Module/UpdateModuleManifest.Tests.ps1

@@ -0,0 +1,33 @@
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License.
+
+Describe "Update-ModuleManifest tests" -tags "CI" {
+
+    BeforeEach {
+        $testModulePath = "testdrive:/module/test.psd1"
+        New-Item -ItemType Directory -Path testdrive:/module > $null
+    }
+
+    AfterEach {
+        Remove-Item -Recurse -Force -ErrorAction SilentlyContinue testdrive:/module
+    }
+
+    It "Update should not clear out NestedModules: <variation>" -TestCases @(
+        @{ variation = "export with wildcards"; exportValue = "*" },
+        @{ variation = "export without wildcards"; exportValue = "@()"}
+    ) {
+        param($exportValue)
+
+        New-Item -ItemType File -Path testdrive:/module/foo.psm1 > $null
+        New-ModuleManifest -Path $testModulePath -NestedModules foo.psm1 -HelpInfoUri http://foo.com -AliasesToExport $exportValue -CmdletsToExport $exportValue -FunctionsToExport $exportValue -VariablesToExport $exportValue -DscResourcesToExport $exportValue
+        $module = Test-ModuleManifest -Path $testModulePath
+        $module.HelpInfoUri | Should -BeExactly "http://foo.com/"
+        $module.NestedModules | Should -HaveCount 1
+        $module.NestedModules.Name | Should -BeExactly foo
+        Update-ModuleManifest -Path $testModulePath -HelpInfoUri https://bar.org
+        $module = Test-ModuleManifest -Path $testModulePath
+        $module.HelpInfoUri | Should -BeExactly "https://bar.org/"
+        $module.NestedModules | Should -HaveCount 1
+        $module.NestedModules.Name | Should -BeExactly foo
+    }
+}