Add error case tests for File.path

- for non-String argument
- for NUL-contained argument
- for ASCII-incompatible argument

Author: nobu

spec/ruby/core/file/path_spec.rb

@@ -37,4 +37,45 @@
     path.should_receive(:to_path).and_return("abc")
     File.path(path).should == "abc"
   end
+
+  it "raises TypeError when #to_path result is not a string" do
+    path = mock("path")
+    path.should_receive(:to_path).and_return(nil)
+    -> { File.path(path) }.should raise_error TypeError
+
+    path = mock("path")
+    path.should_receive(:to_path).and_return(42)
+    -> { File.path(path) }.should raise_error TypeError
+  end
+
+  it "raises ArgumentError for string argument contains NUL character" do
+    -> { File.path("\0") }.should raise_error ArgumentError
+    -> { File.path("a\0") }.should raise_error ArgumentError
+    -> { File.path("a\0c") }.should raise_error ArgumentError
+  end
+
+  it "raises ArgumentError when #to_path result contains NUL character" do
+    path = mock("path")
+    path.should_receive(:to_path).and_return("\0")
+    -> { File.path(path) }.should raise_error ArgumentError
+
+    path = mock("path")
+    path.should_receive(:to_path).and_return("a\0")
+    -> { File.path(path) }.should raise_error ArgumentError
+
+    path = mock("path")
+    path.should_receive(:to_path).and_return("a\0c")
+    -> { File.path(path) }.should raise_error ArgumentError
+  end
+
+  it "raises Encoding::CompatibilityError for ASCII-incompatible string argument" do
+    path = "abc".encode(Encoding::UTF_32BE)
+    -> { File.path(path) }.should raise_error Encoding::CompatibilityError
+  end
+
+  it "raises Encoding::CompatibilityError when #to_path result is ASCII-incompatible" do
+    path = mock("path")
+    path.should_receive(:to_path).and_return("abc".encode(Encoding::UTF_32BE))
+    -> { File.path(path) }.should raise_error Encoding::CompatibilityError
+  end
 end

test/ruby/test_file_exhaustive.rb

@@ -204,12 +204,21 @@ def test_path
     end
 
     conv_error = ->(method, msg = "converting with #{method}") {
-      o = Struct.new(method).new(42)
-      assert_raise(TypeError, msg) {File.path(o)}
-      o = Struct.new(method).new("abc".encode(Encoding::UTF_32BE))
-      assert_raise(Encoding::CompatibilityError, msg) {File.path(o)}
-      o = Struct.new(method).new("\0")
-      assert_raise(ArgumentError, msg) {File.path(o)}
+      test = ->(&new) do
+        o = new.(42)
+        assert_raise(TypeError, msg) {File.path(o)}
+
+        o = new.("abc".encode(Encoding::UTF_32BE))
+        assert_raise(Encoding::CompatibilityError, msg) {File.path(o)}
+
+        ["\0", "a\0", "a\0c"].each do |path|
+          o = new.(path)
+          assert_raise(ArgumentError, msg) {File.path(o)}
+        end
+      end
+
+      test.call(&:itself)
+      test.call(&Struct.new(method).method(:new))
     }
 
     conv_error[:to_path]