Improve test coverage

* Refactor some functions to improve unit test coverage.

* Use the "coverage" module if available along with unit tests.

Makefile

@@ -19,6 +19,12 @@ RPM_VERSION := $(VERSION)-$(RPM_RELEASE)
 DEB_VERSION := $(VERSION)~rc$(RELEASE)
 endif
 
+# Python stuff
+PYTHON ?= python3
+PYLINT ?= pylint
+BLACK ?= black
+
+HAVE_COVERAGE := $(shell $(PYTHON) -c 'import coverage' 2>/dev/null && echo yes)
 
 # Where packages are built
 BUILD_DIR := build
@@ -82,19 +88,23 @@ clean:
 
 # Check for lint
 lint:
-	pylint src/pgmon.py
-	pylint src/test_pgmon.py
-	black --check --diff src/pgmon.py
-	black --check --diff src/test_pgmon.py
+	$(PYLINT) src/pgmon.py
+	$(PYLINT) src/test_pgmon.py
+	$(BLACK) --check --diff src/pgmon.py
+	$(BLACK) --check --diff src/test_pgmon.py
 
 # Format the code using black
 format:
-	black src/pgmon.py
-	black src/test_pylint.py
+	$(BLACK) src/pgmon.py
+	$(BLACK) src/test_pgmon.py
 
 # Run unit tests for the script
 test:
-	cd src ; python3 -m unittest
+ifeq ($(HAVE_COVERAGE),yes)
+	cd src ; $(PYTHON) -m coverage run -m unittest && python3 -m coverage report -m
+else
+	cd src ; $(PYTHON) -m unittest
+endif
 
 # Run query tests
 query-tests: