1 files changed, 90 insertions, 0 deletions
diff --git a/spec/ruby/core/string/succ_spec.rb b/spec/ruby/core/string/succ_spec.rb
new file mode 100644
index 0000000000..87beca8b09
--- /dev/null
+++ b/spec/ruby/core/string/succ_spec.rb
@@ -0,0 +1,90 @@
+# encoding: binary
+require_relative '../../spec_helper'
+require_relative 'fixtures/classes'
+
+describe "String#succ" do
+  it "returns an empty string for empty strings" do
+    "".succ.should == ""
+  end
+
+  it "returns the successor by increasing the rightmost alphanumeric (digit => digit, letter => letter with same case)" do
+    "abcd".succ.should == "abce"
+    "THX1138".succ.should == "THX1139"
+
+    "<<koala>>".succ.should == "<<koalb>>"
+    "==A??".succ.should == "==B??"
+  end
+
+  it "increases non-alphanumerics (via ascii rules) if there are no alphanumerics" do
+    "***".succ.should == "**+"
+    "**`".succ.should == "**a"
+  end
+
+  it "increases the next best alphanumeric (jumping over non-alphanumerics) if there is a carry" do
+    "dz".succ.should == "ea"
+    "HZ".succ.should == "IA"
+    "49".succ.should == "50"
+
+    "izz".succ.should == "jaa"
+    "IZZ".succ.should == "JAA"
+    "699".succ.should == "700"
+
+    "6Z99z99Z".succ.should == "7A00a00A"
+
+    "1999zzz".succ.should == "2000aaa"
+    "NZ/[]ZZZ9999".succ.should == "OA/[]AAA0000"
+  end
+
+  it "increases the next best character if there is a carry for non-alphanumerics" do
+    "(\xFF".succ.should == ")\x00"
+    "`\xFF".succ.should == "a\x00"
+    "<\xFF\xFF".succ.should == "=\x00\x00"
+  end
+
+  it "adds an additional character (just left to the last increased one) if there is a carry and no character left to increase" do
+    "z".succ.should == "aa"
+    "Z".succ.should == "AA"
+    "9".succ.should == "10"
+
+    "zz".succ.should == "aaa"
+    "ZZ".succ.should == "AAA"
+    "99".succ.should == "100"
+
+    "9Z99z99Z".succ.should == "10A00a00A"
+
+    "ZZZ9999".succ.should == "AAAA0000"
+    "/[]9999".succ.should == "/[]10000"
+    "/[]ZZZ9999".succ.should == "/[]AAAA0000"
+    "Z/[]ZZZ9999".succ.should == "AA/[]AAA0000"
+
+    # non-alphanumeric cases
+    "\xFF".succ.should == "\x01\x00"
+    "\xFF\xFF".succ.should == "\x01\x00\x00"
+  end
+
+  it "returns String instances when called on a subclass" do
+    StringSpecs::MyString.new("").succ.should.instance_of?(String)
+    StringSpecs::MyString.new("a").succ.should.instance_of?(String)
+    StringSpecs::MyString.new("z").succ.should.instance_of?(String)
+  end
+
+  it "returns a String in the same encoding as self" do
+    "z".encode("US-ASCII").succ.encoding.should == Encoding::US_ASCII
+  end
+end
+
+describe "String#succ!" do
+  it "is equivalent to succ, but modifies self in place (still returns self)" do
+    ["", "abcd", "THX1138"].each do |s|
+      s = +s
+      r = s.dup.succ!
+      s.succ!.should.equal?(s)
+      s.should == r
+    end
+  end
+
+  it "raises a FrozenError if self is frozen" do
+    -> { "".freeze.succ!     }.should.raise(FrozenError)
+    -> { "abcd".freeze.succ! }.should.raise(FrozenError)
+  end
+end