Test that add-path packages take priority

This was not currently tested explicitly, and is currently
the reason why we still have the scanning behavior in the
PackageManager.
In order to remove the scanning behavior and have the PM
lazily scan packages, we first must add test to ensure
there will be no further regression.

source/dub/test/other.d

@@ -46,3 +46,36 @@ unittest
     assert(dub.project.hasAllDependencies());
     assert(dub.project.getDependency("dep1", true), "Missing 'dep1' dependency");
 }
+
+// Test for https://github.com/dlang/dub/pull/2481
+// Make sure packages found with `add-path` take priority.
+unittest
+{
+    const AddPathDir = TestDub.Paths.temp ~ "addpath/";
+    const BDir = AddPathDir ~ "b/";
+    scope dub = new TestDub((scope FSEntry root) {
+            root.writeFile(TestDub.ProjectPath ~ "dub.json",
+                `{ "name": "a", "dependencies": { "b": "~>1.0" } }`);
+
+            root.writePackageFile("b", "1.0.0", `name "b"
+version "1.0.0"`, PackageFormat.sdl);
+            root.mkdir(BDir);
+            root.writeFile(BDir ~ "dub.json", `{"name": "b", "version": "1.0.0" }`);
+    });
+
+    dub.loadPackage();
+    assert(!dub.project.hasAllDependencies());
+    dub.upgrade(UpgradeOptions.select);
+    // Test that without add-path, we get a package in the userPackage
+    const oldDir = dub.project.getDependency("b", true).path();
+    assert(oldDir == TestDub.Paths.userPackages ~ "packages/b/1.0.0/b/",
+           oldDir.toNativeString());
+    // Now run `add-path`
+    dub.addSearchPath(AddPathDir.toNativeString(), dub.defaultPlacementLocation);
+    // We need a new instance to test
+    scope newDub = dub.newTest();
+    newDub.loadPackage();
+    assert(newDub.project.hasAllDependencies());
+    const actualDir = newDub.project.getDependency("b", true).path();
+    assert(actualDir == BDir, actualDir.toNativeString());
+}