diff --git a/source/dub/compilers/buildsettings.d b/source/dub/compilers/buildsettings.d
index 16de290..3da87b1 100644
--- a/source/dub/compilers/buildsettings.d
+++ b/source/dub/compilers/buildsettings.d
@@ -108,8 +108,9 @@
 	void removeOptions(in BuildOption[] value...) { foreach (v; value) this.options &= ~v; }
 	void removeOptions(in BuildOptions value) { this.options &= ~value; }
 
+private:
 	// Adds vals to arr without adding duplicates.
-	private void add(ref string[] arr, in string[] vals, bool no_duplicates = true)
+	static void add(ref string[] arr, in string[] vals, bool no_duplicates = true)
 	{
 		if (!no_duplicates) {
 			arr ~= vals;
@@ -127,7 +128,16 @@
 		}
 	}
 
-	private void prepend(ref string[] arr, in string[] vals, bool no_duplicates = true)
+	unittest
+	{
+		auto ary = ["-dip1000", "-vgc"];
+		BuildSettings.add(ary, ["-dip1000", "-vgc"]);
+		assert(ary == ["-dip1000", "-vgc"]);
+		BuildSettings.add(ary, ["-dip1001", "-vgc"], false);
+		assert(ary == ["-dip1000", "-vgc", "-dip1001", "-vgc"]);
+	}
+
+	static void prepend(ref string[] arr, in string[] vals, bool no_duplicates = true)
 	{
 		if (!no_duplicates) {
 			arr = vals ~ arr;
@@ -145,8 +155,17 @@
 		}
 	}
 
+	unittest
+	{
+		auto ary = ["-dip1000", "-vgc"];
+		BuildSettings.prepend(ary, ["-dip1000", "-vgc"]);
+		assert(ary == ["-dip1000", "-vgc"]);
+		BuildSettings.prepend(ary, ["-dip1001", "-vgc"], false);
+		assert(ary == ["-dip1001", "-vgc", "-dip1000", "-vgc"]);
+	}
+
 	// add string import files (avoids file name duplicates in addition to path duplicates)
-	private void addSI(ref string[] arr, in string[] vals)
+	static void addSI(ref string[] arr, in string[] vals)
 	{
 		bool[string] existing;
 		foreach (v; arr) existing[Path(v).head.toString()] = true;
@@ -159,7 +178,16 @@
 		}
 	}
 
-	private void removePaths(ref string[] arr, in string[] vals)
+	unittest
+	{
+		auto ary = ["path/foo.txt"];
+		BuildSettings.addSI(ary, ["path2/foo2.txt"]);
+		assert(ary == ["path/foo.txt", "path2/foo2.txt"]);
+		BuildSettings.addSI(ary, ["path2/foo.txt"]); // no duplicate basenames
+		assert(ary == ["path/foo.txt", "path2/foo2.txt"]);
+	}
+
+	static void removePaths(ref string[] arr, in string[] vals)
 	{
 		bool matches(string s)
 		{
@@ -171,7 +199,18 @@
 		arr = arr.filter!(s => !matches(s))().array();
 	}
 
-	private void remove(ref string[] arr, in string[] vals)
+	unittest
+	{
+		auto ary = ["path1", "root/path1", "root/path2", "root2/path1"];
+		BuildSettings.removePaths(ary, ["path1"]);
+		assert(ary == ["root/path1", "root/path2", "root2/path1"]);
+		BuildSettings.removePaths(ary, ["*/path1"]);
+		assert(ary == ["root/path2"]);
+		BuildSettings.removePaths(ary, ["foo", "bar", "root/path2"]);
+		assert(ary == []);
+	}
+
+	static void remove(ref string[] arr, in string[] vals)
 	{
 		bool matches(string s)
 		{
@@ -182,6 +221,21 @@
 		}
 		arr = arr.filter!(s => !matches(s))().array();
 	}
+
+	unittest
+	{
+		import std.string : join;
+
+		auto ary = ["path1", "root/path1", "root/path2", "root2/path1"];
+		BuildSettings.remove(ary, ["path1"]);
+		assert(ary == ["root/path1", "root/path2", "root2/path1"]);
+		BuildSettings.remove(ary, ["root/path*"]);
+		assert(ary == ["root/path1", "root/path2", "root2/path1"]);
+		BuildSettings.removePaths(ary, ["foo", "root/path2", "bar", "root2/path1"]);
+		assert(ary == ["root/path1"]);
+		BuildSettings.remove(ary, ["root/path1", "foo"]);
+		assert(ary == []);
+	}
 }
 
 enum BuildSetting {