Add an unit test for #678

This is an unit test for the issue with multiple downloads and installs
of the same dependency package.

Related to #678

tests/issue678/issue678.nimble

@@ -0,0 +1,12 @@
+# Package
+
+version     = "0.1.0"
+author      = "Ivan Bobev"
+description = "Package for ensuring that issue #678 is resolved."
+license     = "MIT"
+
+# Dependencies
+
+requires "nim >= 0.19.6"
+# to reproduce dependency 2 must be before 1
+requires "issue678_dependency_2", "issue678_dependency_1"

tests/issue678/packages.json

@@ -0,0 +1,19 @@
+[
+  {
+    "name": "issue678_dependency_1",
+    "url": "https://github.com/bobeff/issue678?subdir=dependency_1",
+    "method": "git",
+    "tags": [ "test" ], 
+    "description":
+      "Both first and second level dependency of the issue678 package.",
+    "license": "MIT"
+  },
+  {
+    "name": "issue678_dependency_2",
+    "url": "https://github.com/bobeff/issue678?subdir=dependency_2",
+    "method": "git",
+    "tags": [ "test" ],
+    "description": "First level dependency of the issue678 package.",
+    "license": "MIT"
+  }
+]