Document the platform configuration (dotnet#42185)

Co-authored-by: Genevieve Warren <[email protected]>

docs/core/testing/unit-testing-platform-config.md

@@ -0,0 +1,40 @@
+---
+title: Microsoft.Testing.Platform config options
+description: Learn how to configure Microsoft.Testing.Platform using configuration settings.
+author: Evangelink
+ms.author: amauryleve
+ms.date: 08/15/2024
+---
+
+# Microsoft.Testing.Platform configuration settings
+
+Microsoft.Testing.Platform supports the use of configuration files and environment variables to configure the behavior of the test platform. This article describes the configuration settings that you can use to configure the test platform.
+
+## testconfig.json
+
+The test platform uses a configuration file named *[appname].testconfig.json* to configure the behavior of the test platform. The *testconfig.json* file is a JSON file that contains configuration settings for the test platform.
+
+The *testconfig.json* file has the following structure:
+
+```json
+{
+    "platformOptions": {
+        "config-property-name1": "config-value1",
+        "config-property-name2": "config-value2"
+    }
+}
+```
+
+The platform will automatically detect and load the *[appname].testconfig.json* file located in the output directory of the test project (close to the executable).
+
+When using [Microsoft.Testing.Platform.MSBuild](https://www.nuget.org/packages/Microsoft.Testing.Platform.MSBuild), you can simply create a *testconfig.json* file that will be automatically renamed to *[appname].testconfig.json* and moved to the output directory of the test project.
+
+> [!NOTE]
+> The *[appname].testconfig.json* file will get overwritten on subsequent builds.
+
+## Environment variables
+
+Environment variables can be used to supply some runtime configuration information.
+
+> [!NOTE]
+> Environment variables take precedence over configuration settings in the *testconfig.json* file.

docs/navigate/devops-testing/toc.yml

@@ -179,6 +179,8 @@ items:
             href: ../../core/testing/unit-testing-platform-faq.md
           - name: Comparison with VSTest
             href: ../../core/testing/unit-testing-platform-vs-vstest.md
+          - name: Configure the test platform
+            href: ../../core/testing/unit-testing-platform-config.md
           - name: Extensions
             items:
               - name: Overview