1 files changed, 35 insertions, 0 deletions
diff --git a/spec/ruby/core/set/proper_subset_spec.rb b/spec/ruby/core/set/proper_subset_spec.rb
new file mode 100644
index 0000000000..3fd27da131
--- /dev/null
+++ b/spec/ruby/core/set/proper_subset_spec.rb
@@ -0,0 +1,35 @@
+require_relative '../../spec_helper'
+require_relative 'fixtures/set_like'
+set_version = defined?(Set::VERSION) ? Set::VERSION : '1.0.0'
+
+describe "Set#proper_subset?" do
+  before :each do
+    @set = Set[1, 2, 3, 4]
+  end
+
+  it "returns true if passed a Set that self is a proper subset of" do
+    Set[].proper_subset?(@set).should == true
+    Set[].proper_subset?(Set[1, 2, 3]).should == true
+    Set[].proper_subset?(Set["a", :b, ?c]).should == true
+
+    Set[1, 2, 3].proper_subset?(@set).should == true
+    Set[1, 3].proper_subset?(@set).should == true
+    Set[1, 2].proper_subset?(@set).should == true
+    Set[1].proper_subset?(@set).should == true
+
+    Set[5].proper_subset?(@set).should == false
+    Set[1, 5].proper_subset?(@set).should == false
+    Set[nil].proper_subset?(@set).should == false
+    Set["test"].proper_subset?(@set).should == false
+
+    @set.proper_subset?(@set).should == false
+    Set[].proper_subset?(Set[]).should == false
+  end
+
+  it "raises an ArgumentError when passed a non-Set" do
+    -> { Set[].proper_subset?([]) }.should.raise(ArgumentError)
+    -> { Set[].proper_subset?(1) }.should.raise(ArgumentError)
+    -> { Set[].proper_subset?("test") }.should.raise(ArgumentError)
+    -> { Set[].proper_subset?(Object.new) }.should.raise(ArgumentError)
+  end
+end