Update the Makefile to invoke the examples; add a levels concept to t…

…ests.

The Makefile's default target has been updated so that it now requires
that the 'system' level tests build. This is one of 3 new targets that
have been added:

  - test_level_unittests, which should cause the unit tests to run.
    We don't have any yet, but some will be added shortly.

  - test_level_integration, which causes the integration tests to run.
    These are the tests in the 'tests' directory, which exercise the
    external interface in a test-like environment to see that it
    functions as desired.
    This level is dependant on the unittests passing before it will
    be run.

  - test_level_system, which causes the examples to be run.
    These examples are the sorts of programs that a user might write,
    and which we expect to be invoked from the command and to do
    their job.
    This level is dependant on the integration tests passing before
    it will be run.

In CI, the individual test targets (rather than the levels) would
probably be invoked, with each one still dependant on the earlier ones
in stages (or maybe just run them all in parallel, as they're all very
fast).

Makefile

@@ -1,7 +1,7 @@
 # Common User Targets:
 #
 #	make tests
-#		- Sxecute the tests
+#		- Execute the tests
 #
 #	make shell
 #		- Set up the environment and drop to a shell (re-uses existing shells if they
@@ -40,12 +40,34 @@ NOTICE = @notice() { printf "\n${COL_NOTICE}+++ %s${COL_RESET}\n" "$$@"; } && no
 GOOD = @notice() { printf "\n${COL_GOOD}+++ %s${COL_RESET}\n" "$$@"; } && notice
 
 
-tests: test_testable
-	${NOTICE} "Running tests"
+tests: test_level_system
+	${GOOD} "All tests passed"
+
+# 'test_level_*' targets run all the tests up to that level
+test_level_unittests: unittests
+test_level_integration: test_level_unittests integrationtests
+test_level_system: test_level_integration systemtests
+
+# Unit tests test individual parse of a small unit.
+unittests: test_testable
+	${NOTICE} "Running unit tests"
+	${GOOD} "Unit tests passed (we don't have any yet)"
+
+# Integration tests check the integration of those units.
+integrationtests: test_testable
+	${NOTICE} "Running integration tests"
 	@# Note: We cd into the tests directory, so that we are testing the installed version, not
 	@# 		the version in the repository.
 	${ACTIVATE} && cd tests && python -munittest -v ${TEST_MODULES}
-	${GOOD} "Tests passed"
+	${GOOD} "Integration tests passed"
+
+# System tests check that the way that a user might use it works.
+systemtests: test_testable
+	${NOTICE} "Running system tests"
+	@# We only run 1000 runs; just enough that we get to see that it's running the tests.
+	${ACTIVATE} && examples/run_all_examples.py --runs 1000
+	${GOOD} "System tests passed"
+
 
 venv: venv/successful-${PYTHON_TOOL}