test(error): add inner error tests

Author: kevinhwang91

spec/error_spec.lua

@@ -0,0 +1,63 @@
+local e = require('promise-async.error')
+local basics = require('spec.helpers.basics')
+
+describe('Error for Promise and Async.', function()
+    describe('Basic operations about error,', function()
+        local msg = 'message test'
+        it('create a error', function()
+            local err = e:new(msg)
+            assert.equal(msg, tostring(err))
+        end)
+
+        it('append messages to a error', function()
+            local err = e:new(msg)
+            err:push('foo')
+            err:push('bar')
+            assert.equal('message test\nstack traceback:\nfoo\nbar', tostring(err))
+        end)
+
+        it('do unshift for a error', function()
+            local err = e:new(msg)
+            err:push('foo')
+            err:push('bar')
+            err:unshift('UnhandledPromiseRejection baz:')
+            assert.equal('UnhandledPromiseRejection baz:\nmessage test\nstack traceback:\nfoo\nbar', tostring(err))
+        end)
+    end)
+
+    describe('Build stacks.', function()
+        describe('Build basic values for top of stack.', function()
+            -- keep stack always from tail calls
+            local function level3(v)
+                local s = e:new(v):buildStack(2, '[C]')
+                return tostring(s)
+            end
+            local function level2(v)
+                local o = level3(v)
+                return o
+            end
+            local function level1(v)
+                local o = level2(v)
+                return o
+            end
+            local src = debug.getinfo(1).short_src
+            local level1Line = debug.getinfo(level1, 'S').linedefined
+            local level2Line = debug.getinfo(level2, 'S').linedefined
+            local level3Line = debug.getinfo(level3, 'S').linedefined
+            local stackStr = ([[stack traceback:
+	%s:%d: in function 'level3'
+	%s:%d: in function 'level2'
+	%s:%d: in function 'level1']]):format(src, level3Line + 1, src, level2Line + 1, src, level1Line + 1)
+            local function testBasicTopStack(expectedValue, stringRepresentation)
+                it('The value is ' .. stringRepresentation .. '.', function()
+                    local s = level1(expectedValue)
+                    assert.equal(tostring(expectedValue) .. '\n' .. stackStr, s)
+                end)
+            end
+
+            for valueStr, basicFn in pairs(basics) do
+                testBasicTopStack(basicFn(), valueStr)
+            end
+        end)
+    end)
+end)

spec/helpers/basics.lua

@@ -20,7 +20,11 @@ Basic['`string`'] = function()
 end
 
 Basic['a metatable'] = function()
-    return setmetatable({}, {})
+    return setmetatable({}, {
+        __tostring = function()
+            return '{}'
+        end
+    })
 end
 
 Basic['a thread'] = function()