have the generated packages break/replace each other

2 files changed, 36 insertions, 16 deletions

diff --git a/hwpack/hardwarepack.py b/hwpack/hardwarepack.py
index 53cbf0c..64f559e 100644
--- a/hwpack/hardwarepack.py
+++ b/hwpack/hardwarepack.py
@@ -164,33 +164,45 @@ class HardwarePack(object):
         self.packages += packages
 
     def add_dependency_packages(self, packages_spec):
-        """XXX Add a package that depends on packages_spec to the hardware pack.
+        """Add package that depends on those already present to the pack.
 
-        The added package will share the name, version and architecture of the
-        hardware pack itself.
+        This method will add two packages.  One will be called 'hwpack-' + the
+        name of the pack and will depend on the exact versions of every
+        package in the hwpack.  The other will have -latest appended to the
+        name and will depend on `package_spec`, which is assumed to be the
+        package specification the hardware pack was built with.
+
+        The added packages will share version and architecture of the hardware
+        pack itself and will Replace/Break each other.
 
         :param packages_spec: A list of apt package specifications,
             e.g. ``['foo', 'bar (>= 1.2)']``.
         """
         with PackageMaker() as maker:
+            dep_package_name = 'hwpack-' + self.metadata.name
+            latest_dep_package_name = dep_package_name + '-latest'
+
+            dep_relationships = {
+                'Replaces': latest_dep_package_name,
+                'Breaks': latest_dep_package_name
+                }
             deps = ['%s (= %s)'%(p.name, p.version) for p in self.packages]
             if deps:
-                relationships = {'Depends': ', '.join(deps)}
-            else:
-                relationships = {}
+                dep_relationships['Depends'] = ', '.join(deps)
             deb_file_path = maker.make_package(
-                'hwpack-' + self.metadata.name, self.metadata.version,
-                relationships, self.metadata.architecture)
+                dep_package_name, self.metadata.version,
+                dep_relationships, self.metadata.architecture)
             self.packages.append(FetchedPackage.from_deb(deb_file_path))
 
+            latest_dep_relationships = {
+                'Replaces': dep_package_name,
+                'Breaks': dep_package_name
+                }
             if packages_spec:
-                relationships = {'Depends': ', '.join(packages_spec)}
-            else:
-                relationships = {}
+                latest_dep_relationships['Depends'] = ', '.join(packages_spec)
             deb_file_path = maker.make_package(
-                'hwpack-' + self.metadata.name + '-latest',
-                self.metadata.version, relationships,
-                self.metadata.architecture)
+                latest_dep_package_name, self.metadata.version,
+                latest_dep_relationships, self.metadata.architecture)
             self.packages.append(FetchedPackage.from_deb(deb_file_path))
 
     def to_file(self, fileobj):
diff --git a/hwpack/tests/test_hardwarepack.py b/hwpack/tests/test_hardwarepack.py
index 5b3faed..ddca484 100644
--- a/hwpack/tests/test_hardwarepack.py
+++ b/hwpack/tests/test_hardwarepack.py
@@ -230,27 +230,35 @@ class HardwarePackTests(TestCase):
             Not(HardwarePackHasFile("pkgs/%s" % package1.filename)))
 
     def matcher_for_dependency_package(self, metadata, packages):
+        dep_package_name = 'hwpack-%s' % metadata.name
+        latest_dep_package_name = 'hwpack-%s-latest' % metadata.name
         if packages == []:
             dep_matcher = Equals(None)
         else:
             dep_matcher = MatchesPackageRelationshipList(
                 [Equals('%s (= %s)' % (p.name, p.version)) for p in packages])
         return MatchesStructure(
-            name=Equals('hwpack-' + self.metadata.name),
+            name=Equals(dep_package_name),
             architecture=Equals(self.metadata.architecture),
+            breaks=Equals(latest_dep_package_name),
+            replaces=Equals(latest_dep_package_name),
             depends=dep_matcher,
             version=Equals(self.metadata.version))
 
     def matcher_for_latest_dependency_package(self, metadata, package_spec):
+        dep_package_name = 'hwpack-%s' % metadata.name
+        latest_dep_package_name = 'hwpack-%s-latest' % metadata.name
         if package_spec == []:
             dep_matcher = Equals(None)
         else:
             dep_matcher = MatchesPackageRelationshipList(
                 [Equals(p) for p in package_spec])
         return MatchesStructure(
-            name=Equals('hwpack-' + metadata.name + '-latest'),
+            name=Equals(latest_dep_package_name),
             architecture=Equals(metadata.architecture),
             depends=dep_matcher,
+            breaks=Equals(dep_package_name),
+            replaces=Equals(dep_package_name),
             version=Equals(metadata.version))
 
     def test_add_dependency_package_adds_packages(self):