diff --git a/Library/Homebrew/test/os/linux/formula_spec.rb b/Library/Homebrew/test/os/linux/formula_spec.rb
index 806e4a3f77..6a38602109 100644
--- a/Library/Homebrew/test/os/linux/formula_spec.rb
+++ b/Library/Homebrew/test/os/linux/formula_spec.rb
@@ -107,6 +107,12 @@ describe Formula do
       f = Testball.new
       expect(f.shared_library("foobar")).to eq("foobar.so")
       expect(f.shared_library("foobar", 2)).to eq("foobar.so.2")
+      expect(f.shared_library("foobar", nil)).to eq("foobar.so")
+      expect(f.shared_library("foobar", "*")).to eq("foobar.so{,.*}")
+      expect(f.shared_library("*")).to eq("*.so{,.*}")
+      expect(f.shared_library("*", 2)).to eq("*.so.2")
+      expect(f.shared_library("*", nil)).to eq("*.so{,.*}")
+      expect(f.shared_library("*", "*")).to eq("*.so{,.*}")
     end
   end
 end
diff --git a/Library/Homebrew/test/os/mac/formula_spec.rb b/Library/Homebrew/test/os/mac/formula_spec.rb
index b33878dc4d..f41812a072 100644
--- a/Library/Homebrew/test/os/mac/formula_spec.rb
+++ b/Library/Homebrew/test/os/mac/formula_spec.rb
@@ -112,6 +112,12 @@ describe Formula do
       f = Testball.new
       expect(f.shared_library("foobar")).to eq("foobar.dylib")
       expect(f.shared_library("foobar", 2)).to eq("foobar.2.dylib")
+      expect(f.shared_library("foobar", nil)).to eq("foobar.dylib")
+      expect(f.shared_library("foobar", "*")).to eq("foobar{,.*}.dylib")
+      expect(f.shared_library("*")).to eq("*.dylib")
+      expect(f.shared_library("*", 2)).to eq("*.2.dylib")
+      expect(f.shared_library("*", nil)).to eq("*.dylib")
+      expect(f.shared_library("*", "*")).to eq("*.dylib")
     end
   end
 end