Add introduction / getting started with testing (incomplete)

Author: aedart

docs/+current/modules/testing/cmake/index.md

@@ -0,0 +1,108 @@
+---
+title: Modules & Scripts
+description: How to write tests for your CMake modules and scripts
+keywords: testing, cmake
+author: RSP Systems A/S
+---
+
+# Testing CMake Modules & Scripts
+
+The `testing` module includes a "_mini_" framework for testing your CMake modules and scripts. It is built on top of
+[CTest](https://cmake.org/cmake/help/latest/manual/ctest.1.html#manual:ctest(1)).
+
+[TOC]
+
+## Getting Started
+
+The following guide illustrates how you can get started. It is by no means a comprehensive guide on how to write tests,
+but rather just a starting point.
+
+### Directory Structure
+
+Create an appropriate directory in which your tests should reside. For instance, this can be located in the root
+of your project. You can name it "tests", or whatever makes the most sense for you. The important part is to isolate
+tests from the remaining of your project's CMake logic.
+
+The following example is a possible directory and files structure, that you can use.
+
+```
+/tests
+    /unit
+        /assets
+            build_assets_test.cmake
+    CMakeLists.txt    
+CMakeLists.txt
+```
+
+### Define Test Suite
+
+In your `/tests/CMakeLists.txt`, define the [test suite(s)](./01_test_suite.md) for your project.
+
+```cmake
+# ...in your /tests/CMakeLists.txt
+
+enable_testing()
+
+project(my_package_tests LANGUAGES NONE)
+
+include("rsp/testing")
+
+# Define the test suites for this project
+define_test_suite("unit" DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/unit")
+```
+
+### Define Test Case
+
+To define a new test case, invoke the [`define_test_case()`](./02_test_case.md) function.
+This should be done in each test file (_e.g. in the `/tests/unit/assets/build_assets_tests.cmake` from the above
+shown example directory and files structure)._
+
+```cmake
+# ... in your test file
+
+include("rsp/testing")
+
+define_test_case(
+    "Build Assets Test"
+    LABELS "assets;build"
+)
+
+# ... remaining not shown ...
+```
+
+### Define Test(s)
+
+Once your test-case has been defined, you can define the tests. To do so, you need to define the function that must
+be invoked when the test-case is executed. This is done by the [`define_test()`](./03_test.md) function.
+
+```cmake
+# ... in your test file
+
+# ... previous not shown ...
+
+define_test("can build assets" "can_build_assets")
+function(can_build_assets)
+    
+    # ... testing logic not shown ...
+    
+    assert_truthy(assets_built MESSAGE "Assets could bot be built...")
+endfunction()
+
+define_test("fails if assets not ready" "fails_when_not_ready" EXPECT_FAILURE)
+function(fails_when_not_ready)
+
+    # ... testing logic not shown ...
+
+    assert_truthy(false MESSAGE "Assets should not be built when not ready...")
+endfunction()
+
+# ... etc
+```
+
+### Build & Run
+
+_TODO: ..._
+
+## Caveats
+
+_TODO: ..._