Refine the docs.
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+# Testing
+
+Testing of Hafnium is currently evolving. There are basic tests running on QEMU
+but we want more and more kinds of tests e.g. unit tests.
+
+## Presubmit
+
+Presubmit builds everything, runs all tests and checks the source for
+formatting and lint errors. This can be run locally with:
+
+``` shell
+./kokoro/ubuntu/build.sh
+```
+
+Or to just run the tests after having built everything manually run:
+
+``` shell
+./kokoro/ubuntu/test.sh
+```
+
+## QEMU tests
+
+These tests boot Hafnium on QEMU and the VMs make calls to Hafnium to test its
+behaviour.
+
+### `hftest`
+
+Having a framework for tests makes them easier to read and write. `hftest` in a
+framework to meet the needs of VM based tests for Hafnium. It consists of:
+
+ * assertions
+ * test declarations
+ * base VM image
+ * driver script
+
+Assertions should be familiar from other testing libraries. They make use of
+C11's `_Generic` expressions for type genericity.
+
+Test declarations name the test and the suite that the test is part of.
+Declarations are converted into descriptors stored in the `.hftest` section of
+the VM image which allows the image to inspect the structure of the tests it
+contains. The linker sorts the descriptors by their symbol name which is how
+descriptors from the same suite are grouped together for easier parsing.
+
+The base VM image offers a command line interface, via the bootargs, to query
+the tests in the image and to run specific tests. The driver script uses this
+interface to execute tests, each with a fresh QEMU boot to give a fresh
+environment.