util.strbitop: Add tests covering basics

Also as docs

spec/util_strbitop.lua

@@ -0,0 +1,41 @@
+local strbitop = require "util.strbitop";
+describe("util.strbitop", function ()
+	describe("sand()", function ()
+		it("works", function ()
+			assert.equal(string.rep("Aa", 100), strbitop.sand(string.rep("a", 200), "Aa"));
+		end);
+		it("returns empty string if first argument is empty", function ()
+			assert.equal("", strbitop.sand("", ""));
+			assert.equal("", strbitop.sand("", "key"));
+		end);
+		it("returns initial string if key is empty", function ()
+			assert.equal("hello", strbitop.sand("hello", ""));
+		end);
+	end);
+
+	describe("sor()", function ()
+		it("works", function ()
+			assert.equal(string.rep("a", 200), strbitop.sor(string.rep("Aa", 100), "a"));
+		end);
+		it("returns empty string if first argument is empty", function ()
+			assert.equal("", strbitop.sor("", ""));
+			assert.equal("", strbitop.sor("", "key"));
+		end);
+		it("returns initial string if key is empty", function ()
+			assert.equal("hello", strbitop.sor("hello", ""));
+		end);
+	end);
+
+	describe("sxor()", function ()
+		it("works", function ()
+			assert.equal(string.rep("Aa", 100), strbitop.sxor(string.rep("a", 200), " \0"));
+		end);
+		it("returns empty string if first argument is empty", function ()
+			assert.equal("", strbitop.sxor("", ""));
+			assert.equal("", strbitop.sxor("", "key"));
+		end);
+		it("returns initial string if key is empty", function ()
+			assert.equal("hello", strbitop.sxor("hello", ""));
+		end);
+	end);
+end);