All kinds of things

- Add modified BSD license
- Initial test runner github action
- Add is_{type} functions
- export kiwi.Error metatable such that it appears like a class.
- Allow Expression.new to take nil for terms
- Initial set of specs

spec/constraint_spec.lua

@@ -0,0 +1,111 @@
+expose("module", function()
+   require("kiwi")
+end)
+
+describe("Constraint", function()
+   local kiwi = require("kiwi")
+
+   describe("construction", function()
+      local v, lhs
+      before_each(function()
+         v = kiwi.Var("foo")
+         lhs = v + 1
+      end)
+
+      it("has correct type", function()
+         assert.True(kiwi.is_constraint(kiwi.Constraint()))
+         assert.False(kiwi.is_constraint(v))
+      end)
+
+      it("default op and strength", function()
+         local c = kiwi.Constraint(lhs)
+         assert.equal("EQ", c:op())
+         assert.equal(kiwi.strength.REQUIRED, c:strength())
+      end)
+
+      it("configure op", function()
+         local c = kiwi.Constraint(lhs, nil, "LE")
+         assert.equal("LE", c:op())
+      end)
+      it("configure strength", function()
+         local c = kiwi.Constraint(lhs, nil, "GE", kiwi.strength.STRONG)
+         assert.equal(kiwi.strength.STRONG, c:strength())
+      end)
+
+      it("formats well", function()
+         local c = kiwi.Constraint(lhs)
+         assert.equal("1 foo + 1 == 0 | required", tostring(c))
+
+         c = kiwi.Constraint(lhs * 2, nil, "GE", kiwi.strength.STRONG)
+         assert.equal("2 foo + 2 >= 0 | strong", tostring(c))
+
+         c = kiwi.Constraint(lhs / 2, nil, "LE", kiwi.strength.MEDIUM)
+         assert.equal("0.5 foo + 0.5 <= 0 | medium", tostring(c))
+
+         c = kiwi.Constraint(lhs, kiwi.Expression(nil, 3), "GE", kiwi.strength.WEAK)
+         assert.equal("1 foo + -2 >= 0 | weak", tostring(c))
+      end)
+
+      it("rejects invalid args", function()
+         assert.error(function()
+            local _ = kiwi.Constraint(1)
+         end)
+         assert.error(function()
+            local _ = kiwi.Constraint(lhs, 1)
+         end)
+         assert.error(function()
+            local _ = kiwi.Constraint("")
+         end)
+         assert.error(function()
+            local _ = kiwi.Constraint(lhs, "")
+         end)
+         assert.error(function()
+            local _ = kiwi.Constraint(lhs, nil, "foo")
+         end)
+         assert.error(function()
+            local _ = kiwi.Constraint(lhs, nil, "LE", "foo")
+         end)
+      end)
+      it("combines lhs and rhs", function()
+         local v2 = kiwi.Var("bar")
+         local rhs = kiwi.Expression({ 5 * v2, 3 * v }, 3)
+         local c = kiwi.Constraint(lhs, rhs)
+
+         local e = c:expression()
+         local t = e:terms()
+         assert.equal(2, #t)
+         if t[1].var ~= v then
+            t[1], t[2] = t[2], t[1]
+         end
+         assert.equal(v, t[1].var)
+         assert.equal(-2.0, t[1].coefficient)
+         assert.equal(v2, t[2].var)
+         assert.equal(-5.0, t[2].coefficient)
+         assert.equal(-2.0, e.constant)
+      end)
+   end)
+
+   describe("method", function()
+      local c, v
+
+      before_each(function()
+         v = kiwi.Var("foo")
+         c = kiwi.Constraint(2 * v + 1)
+      end)
+
+      it("violated", function()
+         assert.True(c:violated())
+         v:set(-0.5)
+         assert.False(c:violated())
+      end)
+
+      it("add/remove constraint", function()
+         local s = kiwi.Solver()
+         c:add_to(s)
+         assert.True(s:has_constraint(c))
+
+         c:remove_from(s)
+         assert.False(s:has_constraint(c))
+      end)
+   end)
+end)