diff --git a/Dockerfile b/Dockerfile
index 7c667c01f82d05cff52d3f7fe986090c89db6565..b69f7f3bf68d4c5728fe206f1bf198ac6af4016a 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -43,4 +43,4 @@ WORKDIR /volume
 ENV HOME /volume
 # Run a test build.
 COPY example/ /example/
-RUN make -C /example all clean
+RUN make --debug=j --keep-going -C /example test
diff --git a/example/Makefile b/example/Makefile
index 52561a323163ba8901b0167564bc2f4d85ef9700..f7e8c094a8160b1ac50421d9789e0d092fe9c583 100644
--- a/example/Makefile
+++ b/example/Makefile
@@ -1,5 +1,7 @@
-.PHONY: all clean
+.PHONY: test
+test: clean all
 
+.PHONY: all
 all: presentation.pdf left-to-right.pdf
 
 presentation.pdf: diagram.pdf
@@ -17,5 +19,6 @@ left-to-right.pdf: left-to-right.md
 %.gif: %.tty
 	ttyrec2gif -in $< -out $@
 
+.PHONY: clean
 clean:
 	- rm *.pdf *.gif