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"
+  }
+]

tests/tester.nim

@@ -844,3 +844,19 @@ test "remove skips packages with revDeps (#504)":
 test "pass options to the compiler with `nimble install`":
   cd "passNimFlags":
     check execNimble("install", "--passNim:-d:passNimIsWorking").exitCode == QuitSuccess
+
+test "do not install single dependency multiple times (#678)":
+  # for the test to be correct, the tested package and its dependencies must not
+  # exist in the local cache
+  removeDir("nimbleDir")
+  cd "issue678":
+    testRefresh():
+      writeFile(configFile, """
+        [PackageList]
+        name = "local"
+        path = "$1"
+      """.unindent % (getCurrentDir() / "packages.json").replace("\\", "\\\\"))
+      check execNimble(["refresh"]).exitCode == QuitSuccess
+      let (output, exitCode) = execNimble("install", "-y")
+      check exitCode == QuitSuccess
+      check output.find("issue678_dependency_1@0.1.0 already exists") == -1