Merge pull request #394 from stfc/fix-graphviz-detection

Fix graphviz detection

changelog

@@ -147,9 +147,13 @@
 
         46) PR #370 for #339. Makes the support for operators in the PSyIR
         more robust by using an enumerator. Adds support for some intrinsics.
+
         47) PR #389 for #386. Variable names and associated loop-types
 	for the NEMO API are now stored in the configuration file.
 
+        48) PR #394 for #392. Fixes a bug in the way the test suite checks
+	for whether the graphviz package is available.
+
 release 1.7.0 20th December 2018
 
 	1) #172 and PR #173 Add support for logical declaration, the save

src/psyclone/tests/conftest.py

@@ -75,8 +75,12 @@ def have_graphviz():
     ''' Whether or not the system has graphviz installed. Note that this
     only checks for the Python bindings. The underlying library must
     also have been installed for dag generation to work correctly. '''
-    import sys
-    return "graphviz" in sys.modules
+    try:
+        # pylint: disable=unused-variable
+        import graphviz
+    except ImportError:
+        return False
+    return True
 
 
 @pytest.fixture(scope="session", autouse=True)