test_tab: add test for Tab#spec

Fixes Homebrew/homebrew#42147.
Closes Homebrew/homebrew#42205.

Signed-off-by: Xu Cheng <xucheng@me.com>

Library/Homebrew/test/fixtures/receipt.json

@@ -9,9 +9,13 @@
   ],
   "built_as_bottle": false,
   "poured_from_bottle": true,
-  "tapped_from": "Homebrew/homebrew",
   "time": 1403827774,
   "HEAD": "deadbeefdeadbeefdeadbeefdeadbeefdeadbeef",
   "stdlib": "libcxx",
-  "compiler": "clang"
+  "compiler": "clang",
+  "source": {
+      "path": "/usr/local/Library/Formula/foo.rb",
+      "tap": "Homebrew/homebrew",
+      "spec": "stable"
+  }
 }

Library/Homebrew/test/fixtures/receipt_old.json

@@ -0,0 +1,17 @@
+{
+  "used_options": [
+    "--with-foo",
+    "--without-bar"
+  ],
+  "unused_options": [
+    "--with-baz",
+    "--without-qux"
+  ],
+  "built_as_bottle": false,
+  "poured_from_bottle": true,
+  "tapped_from": "Homebrew/homebrew",
+  "time": 1403827774,
+  "HEAD": "deadbeefdeadbeefdeadbeefdeadbeefdeadbeef",
+  "stdlib": "libcxx",
+  "compiler": "clang"
+}

Library/Homebrew/test/test_tab.rb

@@ -19,6 +19,7 @@ class TabTests < Homebrew::TestCase
       "source"             => {
         "tap" => "Homebrew/homebrew",
         "path" => nil,
+        "spec" => "stable",
       },
     })
   end
@@ -66,6 +67,22 @@ class TabTests < Homebrew::TestCase
     assert_predicate @tab, :poured_from_bottle
   end
 
+  def test_from_old_version_file
+    path = Pathname.new(TEST_DIRECTORY).join("fixtures", "receipt_old.json")
+    tab = Tab.from_file(path)
+
+    assert_equal @used.sort, tab.used_options.sort
+    assert_equal @unused.sort, tab.unused_options.sort
+    refute_predicate tab, :built_as_bottle
+    assert_predicate tab, :poured_from_bottle
+    assert_equal "Homebrew/homebrew", tab.tap
+    assert_equal :stable, tab.spec
+    refute_nil tab.time
+    assert_equal TEST_SHA1, tab.HEAD
+    assert_equal :clang, tab.cxxstdlib.compiler
+    assert_equal :libcxx, tab.cxxstdlib.type
+  end
+
   def test_from_file
     path = Pathname.new(TEST_DIRECTORY).join("fixtures", "receipt.json")
     tab = Tab.from_file(path)
@@ -75,6 +92,7 @@ class TabTests < Homebrew::TestCase
     refute_predicate tab, :built_as_bottle
     assert_predicate tab, :poured_from_bottle
     assert_equal "Homebrew/homebrew", tab.tap
+    assert_equal :stable, tab.spec
     refute_nil tab.time
     assert_equal TEST_SHA1, tab.HEAD
     assert_equal :clang, tab.cxxstdlib.compiler
@@ -88,6 +106,7 @@ class TabTests < Homebrew::TestCase
     assert_equal @tab.built_as_bottle, tab.built_as_bottle
     assert_equal @tab.poured_from_bottle, tab.poured_from_bottle
     assert_equal @tab.tap, tab.tap
+    assert_equal @tab.spec, tab.spec
     assert_equal @tab.time, tab.time
     assert_equal @tab.HEAD, tab.HEAD
     assert_equal @tab.compiler, tab.compiler