tests: add cmd/link, cmd/unlink integration tests (#398)

Library/Homebrew/test/test_integration_cmds.rb

@@ -110,11 +110,11 @@ class IntegrationCommandTests < Homebrew::TestCase
     formula_path = CoreTap.new.formula_dir/"#{name}.rb"
 
     case name
-    when "testball"
+    when /^testball/
       content = <<-EOS.undent
         desc "Some test"
         homepage "https://example.com/#{name}"
-        url "file://#{File.expand_path("..", __FILE__)}/tarballs/#{name}-0.1.tbz"
+        url "file://#{File.expand_path("..", __FILE__)}/tarballs/testball-0.1.tbz"
         sha256 "#{TESTBALL_SHA256}"
 
         option "with-foo", "Build with foo"
@@ -665,4 +665,31 @@ class IntegrationCommandTests < Homebrew::TestCase
     assert_equal "Warning: No services available to control with `brew services`",
       cmd("services", "list")
   end
+
+  def test_link
+    assert_match "This command requires a keg argument", cmd_fail("link")
+
+    setup_test_formula "testball1"
+    cmd("install", "testball1")
+    cmd("link", "testball1")
+
+    cmd("unlink", "testball1")
+    assert_match "Would link", cmd("link", "--dry-run", "testball1")
+    assert_match "Would remove",
+      cmd("link", "--dry-run", "--overwrite", "testball1")
+    assert_match "Linking", cmd("link", "testball1")
+
+    setup_test_formula "testball2", <<-EOS.undent
+      keg_only "just because"
+    EOS
+    cmd("install", "testball2")
+    assert_match "testball2 is keg-only", cmd("link", "testball2")
+  end
+
+  def test_unlink
+    setup_test_formula "testball"
+
+    cmd("install", "testball")
+    assert_match "Would remove", cmd("unlink", "--dry-run", "testball")
+  end
 end