increase tests coverage

Author: Picazsoo

modules/openapi-generator/src/test/java/org/openapitools/codegen/TestUtils.java

@@ -173,7 +173,7 @@ public static void assertFileContains(Path path, String... lines) {
             String file = linearize(generatedFile);
             assertNotNull(file);
             for (String line : lines)
-                assertTrue(file.contains(linearize(line)), "File does not contain line [" + line + "]");
+                assertTrue(file.contains(linearize(line)), "File '" + path + "' does not contain line [" + line + "]");
         } catch (IOException e) {
             fail("Unable to evaluate file " + path);
         }