diff --git a/Dockerfile b/Dockerfile
index 68875cb..203a40d 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -15,4 +15,4 @@ ADD makefile.extra.make makefile.extra.make
 
 ENV PYTHONPATH="src/:vendor/"
 
-CMD make serve
+CMD make test_compat
diff --git a/makefile.config.make b/makefile.config.make
index 48184dd..5d15b6f 100644
--- a/makefile.config.make
+++ b/makefile.config.make
@@ -6,7 +6,7 @@ PACKAGE_NAME := pycalver
 # - `make ipy`
 # - `make lint`
 # - `make devtest`
-DEVELOPMENT_PYTHON_VERSION := python=3.6
+DEVELOPMENT_PYTHON_VERSION := python=3.7
 
 # These must be valid (space separated) conda package names.
 # A separate conda environment will be created for each of these.
diff --git a/makefile.extra.make b/makefile.extra.make
index 4d4302b..4ae4ada 100644
--- a/makefile.extra.make
+++ b/makefile.extra.make
@@ -32,6 +32,6 @@ test_compat: $(COMPAT_TEST_FILES)
 	for i in $${!env_pys[@]}; do \
 		env_py=$${env_pys[i]}; \
 		$${env_py} -m pip install --upgrade build/test_wheel/*.whl; \
-		PYTHONPATH="" ENV=$${ENV-dev} \
-			$${env_py} -m pytest --verbose compat_test/; \
+		ENABLE_BACKTRACE=0 PYTHONPATH="" ENV=$${ENV-dev} \
+			$${env_py} -m pytest --verbose compat_test/ -k novcs_bump; \
 	done;
diff --git a/test/test_cli.py b/test/test_cli.py
index 9519d82..db33ead 100644
--- a/test/test_cli.py
+++ b/test/test_cli.py
@@ -372,6 +372,7 @@ def test_novcs_bump(runner):
     with pl.Path("README.md").open() as fh:
         content = fh.read()
         assert calver + ".0002-alpha !\n" in content
+        assert calver[1:] + ".2a0 !\n" in content
 
     result = runner.invoke(pycalver.cli, ['bump', "--verbose", "--release", "beta"])
     assert result.exit_code == 0
@@ -379,6 +380,7 @@ def test_novcs_bump(runner):
     with pl.Path("README.md").open() as fh:
         content = fh.read()
         assert calver + ".0003-beta !\n" in content
+        assert calver[1:] + ".3b0 !\n" in content
 
 
 def test_git_bump(runner):