test: provide Makefile convenience targets

Add convenience targets to `Makefile` which can run common sets of
tests. For now, add a target for pylint, module-unittests,
pipeline-runtime-tests, as well as all tests.

Currently, it is quite cumbersome to run a reasonable test-setup
locally. Pylint invokation is rather complex, the unittests and runtime
tests in ./test are mixed, and not all tests in ./test can necessarily
be run from a development system.

This commit prepares for a simpler setup:

  * Add `make test-pylint` to run pylint as it is run by CI.

  * Add `make test-module` to run all module-unittests. This is meant to
    be fast (preferably close to instant) and easy to run during
    development to do a short check whether there are obvious typos or
    other errors in local changes.
    If we can keep these tests to machine-local requirements, if we
    avoid any sleeps or heavy computations, then this will remain a
    convenient test-suite to run locally without having to wait for
    30min. In other words: We should be able to keep this under 10s (and
    for the long term under 1min) easily.

  * Add `make test-runtime` to run all osbuild pipeline executions. This
    is not meant to be fast, but thorough. This will require external
    sources (preferably limited to a suitable container image with
    everything embedded). This will very likely not be run during
    development, but rather by the CI.

  * Add `make test-all` to run all tests. Very handy for shy people when
    the chance of embarrassing copy-paste mistakes is too high to push
    publicly.

Additionally to these new targets, this PR introduces 2 new directories
in ./test: ./test/mod/ and ./test/run/
These are meant as equivalent to `test-module` and `test-runtime`. The
reason is that preferably we stick to the auto-discovery of `unittest`
to enumerate tests, rather than enrolling our own or having to enumerate
them explicitly somewhere.
However, we need some way to tell `unittest` which test belongs into
which group. The easiest setup is likely to just use sub-directories.
Note that `test-all` picks all tests independently of where they are
put, even if they are in further different sub-modules under ./test.

For now, no tests are moved into the new directories. I expect this to
take a bit, since there are several out-standing PRs that modify ./test.
I intend to do the final move once we agreed on this and we synchronized
our test-modifications.

Makefile

@@ -17,8 +17,12 @@
 BUILDDIR ?= .
 SRCDIR ?= .
 
+PYLINT ?= pylint
+PYTHON3 ?= python3
 RST2MAN ?= rst2man
 
+SHELL = /bin/bash
+
 #
 # Automatic Variables
 #
@@ -74,6 +78,11 @@ help:
 	@echo
 	@echo "    help:               Print this usage information."
 	@echo "    man:                Generate all man-pages"
+	@echo
+	@echo "    test-all:           Run all tests"
+	@echo "    test-pylint:        Run pylint on all sources"
+	@echo "    test-module:        Run all module unit-tests"
+	@echo "    test-runtime:       Run all osbuild pipeline tests"
 
 $(BUILDDIR)/:
 	mkdir -p "$@"
@@ -99,6 +108,44 @@ $(MANPAGES_TROFF): $(BUILDDIR)/docs/%: $(SRCDIR)/docs/%.rst | $(BUILDDIR)/docs/
 .PHONY: man
 man: $(MANPAGES_TROFF)
 
+#
+# Test Suite
+#
+# We use the python `unittest` module for all tests. All the test-sources are
+# located in the `./test/` top-level directory, with `./test/mod/` for module
+# unittests and `./test/run/` for osbuild pipeline runtime tests.
+#
+
+.PHONY: test-units
+test-module:
+	@$(PYTHON3) -m unittest \
+		discover \
+			--start=$(SRCDIR)/test/mod \
+			--top-level-directory=$(SRCDIR) \
+			-v
+
+.PHONY: test-runtime
+test-runtime:
+	@[[ $${EUID} -eq 0 ]] || (echo "Error: Root privileges required!"; exit 1)
+	@$(PYTHON3) -m unittest \
+		discover \
+			--start=$(SRCDIR)/test/run \
+			--top-level-directory=$(SRCDIR) \
+			-v
+
+.PHONY: test-pylint
+test-pylint:
+	@find . -type f -name "*.py" | xargs $(PYLINT)
+	@$(PYLINT) runners/* assemblers/* stages/* sources/*
+
+.PHONY: test
+test-all: test-pylint
+	@$(PYTHON3) -m unittest \
+		discover \
+			--start=$(SRCDIR)/test \
+			--top-level-directory=$(SRCDIR) \
+			-v
+
 #
 # Building packages
 #