Add a json schema for the test.json used in tests

This does a couple of nice things, one is that editors like vscode can
be configured to use this schema to provide auto completion and error
highlighting if invalid values are added or required values are missing.
It also allows us test that the format of the test matrix work in a unit
test, which I've added. It does require that the python jsonschema
package is installed.

1 files changed, 10 insertions, 2 deletions

diff --git a/docs/markdown/Contributing.md b/docs/markdown/Contributing.md
index 6f4c397..5332938 100644
--- a/docs/markdown/Contributing.md
+++ b/docs/markdown/Contributing.md
@@ -294,9 +294,17 @@ Additionally, the `skip_on_env` key can be used to specify a list of environment
 variables. If at least one environment variable in `skip_on_env` is present, all
 matrix entries containing this value are skipped.
 
-Similarly, the `compilers` key can be used to define a set of compilers required
-for this value.
+Similarly, the `compilers` key can be used to define a mapping of compilers to languages that are required for this value.
 
+```json
+{
+  "compilers": {
+    "c": "gcc",
+    "cpp": "gcc",
+    "d": "gdc"
+  }
+}
+```
 
 Specific option combinations can be excluded with the `exclude` section. It should
 be noted that `exclude` does not require exact matches. Instead, any matrix entry