Reorganize directories (#3462)

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* 🚚 rename test folder to tests

docs/mkdocs/docs/api/macros/json_diagnostics.md

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+# JSON_DIAGNOSTICS
+
+```cpp
+#define JSON_DIAGNOSTICS /* value */
+```
+
+This macro enables [extended diagnostics for exception messages](../../home/exceptions.md#extended-diagnostic-messages).
+Possible values are `1` to enable or `0` to disable (default).
+
+When enabled, exception messages contain a [JSON Pointer](../json_pointer/json_pointer.md) to the JSON value that
+triggered the exception. Note that enabling this macro increases the size of every JSON value by one pointer and adds
+some  runtime overhead.
+
+The diagnostics messages can also be controlled with the CMake option `JSON_Diagnostics` (`OFF` by default) which sets
+`JSON_DIAGNOSTICS` accordingly.
+
+## Default definition
+
+The default value is `0` (extended diagnostics are switched off).
+
+```cpp
+#define JSON_DIAGNOSTICS 0
+```
+
+When the macro is not defined, the library will define it to its default value.
+
+## Notes
+
+!!! danger "ABI incompatibility"
+
+    As this macro changes the definition of the `basic_json` object, it MUST be defined in the same way globally, even
+    across different compilation units: `basic_json` objects with differently defined `JSON_DIAGNOSTICS` macros are
+    not compatible!
+
+## Examples
+
+??? example "Example 1: default behavior"
+
+    ```cpp
+    --8<-- "examples/diagnostics_standard.cpp"
+    ```
+    
+    Output:
+
+    ```
+    --8<-- "examples/diagnostics_standard.output"
+    ```
+
+    This exception can be hard to debug if storing the value `#!c "12"` and accessing it is further apart.
+
+??? example "Example 2: extended diagnostic messages"
+
+    ```cpp
+    --8<-- "examples/diagnostics_extended.cpp"
+    ```
+    
+    Output:
+
+    ```
+    --8<-- "examples/diagnostics_extended.output"
+    ```
+
+    Now the exception message contains a JSON Pointer `/address/housenumber` that indicates which value has the wrong type.
+
+## Version history
+
+- Added in version 3.10.0.