add code coverage.

* https://survivejs.com/webpack/techniques/testing/

5 files changed, 575 insertions, 4 deletions

diff --git a/.babelrc b/.babelrc
index 6785fcd..58c2f8b 100644
--- a/.babelrc
+++ b/.babelrc
@@ -13,5 +13,15 @@
         "modules": false,
       }
     ],
-  ]
+  ],
+  "env": {
+    "karma": {
+      "plugins": [
+        [
+          "istanbul",
+          { "exclude": ["tests/*.test.js"] }
+        ]
+      ],
+    },
+  }
 }
diff --git a/.gitignore b/.gitignore
index f7baf9f..a876617 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 node_modules
 dist
 stats.json
+build
diff --git a/karma.conf.js b/karma.conf.js
index 19d0493..a644276 100644
--- a/karma.conf.js
+++ b/karma.conf.js
@@ -1,8 +1,10 @@
 const parts = require("./webpack.parts");
+const path = require("path");
 
 module.exports = config => {
   const tests = "tests/*.test.js";
 
+  process.env.BABEL_ENV = "karma";
   config.set({
     frameworks: ["mocha"],
     files: [
@@ -16,5 +18,10 @@ module.exports = config => {
     webpack: parts.loadJavaScript(),
     singleRun: true,
     browsers: ['Chrome'],
+    reporters: ["coverage"],
+    coverageReporter: {
+      dir: "build",
+      reporters: [{ type: "html" }, { type: "lcov" }],
+    },
   });
 };
diff --git a/package-lock.json b/package-lock.json
index f0b38ba..99a96cf 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1394,6 +1394,12 @@
       "integrity": "sha512-wGUIVQXuehL5TCqQun8OW81jGzAWycqzFF8lFp+GOM5BXLYj3bKNsYC4daB7n6XjCqxQA/qgTJ+8ANR3acjrog==",
       "dev": true
     },
+    "arrify": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/arrify/-/arrify-1.0.1.tgz",
+      "integrity": "sha1-iYUI2iIm84DfkEcoRWhJwVAaSw0=",
+      "dev": true
+    },
     "asn1": {
       "version": "0.2.4",
       "resolved": "https://registry.npmjs.org/asn1/-/asn1-0.2.4.tgz",
@@ -1763,6 +1769,62 @@
         "babel-runtime": "^6.22.0"
       }
     },
+    "babel-plugin-istanbul": {
+      "version": "5.0.1",
+      "resolved": "https://registry.npmjs.org/babel-plugin-istanbul/-/babel-plugin-istanbul-5.0.1.tgz",
+      "integrity": "sha512-MQXE+9sTKevc0S6pfYUdpF5aA9mktCg9Jh9hIl/RriGEuUbUqPOK94VBBAlHsz88yIoQSRfPeblA3cPuudMs6Q==",
+      "dev": true,
+      "requires": {
+        "find-up": "^3.0.0",
+        "istanbul-lib-instrument": "^2.2.0",
+        "test-exclude": "^5.0.0"
+      },
+      "dependencies": {
+        "find-up": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/find-up/-/find-up-3.0.0.tgz",
+          "integrity": "sha512-1yD6RmLI1XBfxugvORwlck6f75tYL+iR0jqwsOrOxMZyGYqUuDhJ0l4AXdO1iX/FTs9cBAMEk1gWSEx1kSbylg==",
+          "dev": true,
+          "requires": {
+            "locate-path": "^3.0.0"
+          }
+        },
+        "locate-path": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/locate-path/-/locate-path-3.0.0.tgz",
+          "integrity": "sha512-7AO748wWnIhNqAuaty2ZWHkQHRSNfPVIsPIfwEOWO22AmaoVrWavlOcMR5nzTLNYvp36X220/maaRsrec1G65A==",
+          "dev": true,
+          "requires": {
+            "p-locate": "^3.0.0",
+            "path-exists": "^3.0.0"
+          }
+        },
+        "p-limit": {
+          "version": "2.0.0",
+          "resolved": "https://registry.npmjs.org/p-limit/-/p-limit-2.0.0.tgz",
+          "integrity": "sha512-fl5s52lI5ahKCernzzIyAP0QAZbGIovtVHGwpcu1Jr/EpzLVDI2myISHwGqK7m8uQFugVWSrbxH7XnhGtvEc+A==",
+          "dev": true,
+          "requires": {
+            "p-try": "^2.0.0"
+          }
+        },
+        "p-locate": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/p-locate/-/p-locate-3.0.0.tgz",
+          "integrity": "sha512-x+12w/To+4GFfgJhBEpiDcLozRJGegY+Ei7/z0tSLkMmxGZNybVMSfWj9aJn8Z5Fc7dBUNJOOVgPv2H7IwulSQ==",
+          "dev": true,
+          "requires": {
+            "p-limit": "^2.0.0"
+          }
+        },
+        "p-try": {
+          "version": "2.0.0",
+          "resolved": "https://registry.npmjs.org/p-try/-/p-try-2.0.0.tgz",
+          "integrity": "sha512-hMp0onDKIajHfIkdRk3P4CdCmErkYAxxDtP3Wx/4nZ3aGlau2VKh3mZpcuFkH27WQkL/3WBCPOktzA9ZOAnMQQ==",
+          "dev": true
+        }
+      }
+    },
     "babel-plugin-syntax-async-functions": {
       "version": "6.13.0",
       "resolved": "http://registry.npmjs.org/babel-plugin-syntax-async-functions/-/babel-plugin-syntax-async-functions-6.13.0.tgz",
@@ -3929,6 +3991,16 @@
       "integrity": "sha1-6vQ5/U1ISK105cx9vvIAZyueNFs=",
       "dev": true
     },
+    "dateformat": {
+      "version": "1.0.12",
+      "resolved": "https://registry.npmjs.org/dateformat/-/dateformat-1.0.12.tgz",
+      "integrity": "sha1-nxJLZ1lMk3/3BpMuSmQsyo27/uk=",
+      "dev": true,
+      "requires": {
+        "get-stdin": "^4.0.1",
+        "meow": "^3.3.0"
+      }
+    },
     "debug": {
       "version": "3.1.0",
       "resolved": "https://registry.npmjs.org/debug/-/debug-3.1.0.tgz",
@@ -3959,6 +4031,12 @@
       "integrity": "sha1-9dJgKStmDghO/0zbyfCK0yR0SLU=",
       "dev": true
     },
+    "deep-is": {
+      "version": "0.1.3",
+      "resolved": "https://registry.npmjs.org/deep-is/-/deep-is-0.1.3.tgz",
+      "integrity": "sha1-s2nW+128E+7PUk+RsHD+7cNXzzQ=",
+      "dev": true
+    },
     "define-properties": {
       "version": "1.1.3",
       "resolved": "https://registry.npmjs.org/define-properties/-/define-properties-1.1.3.tgz",
@@ -4470,6 +4548,43 @@
       "integrity": "sha1-G2HAViGQqN/2rjuyzwIAyhMLhtQ=",
       "dev": true
     },
+    "escodegen": {
+      "version": "1.8.1",
+      "resolved": "https://registry.npmjs.org/escodegen/-/escodegen-1.8.1.tgz",
+      "integrity": "sha1-WltTr0aTEQvrsIZ6o0MN07cKEBg=",
+      "dev": true,
+      "requires": {
+        "esprima": "^2.7.1",
+        "estraverse": "^1.9.1",
+        "esutils": "^2.0.2",
+        "optionator": "^0.8.1",
+        "source-map": "~0.2.0"
+      },
+      "dependencies": {
+        "esprima": {
+          "version": "2.7.3",
+          "resolved": "https://registry.npmjs.org/esprima/-/esprima-2.7.3.tgz",
+          "integrity": "sha1-luO3DVd59q1JzQMmc9HDEnZ7pYE=",
+          "dev": true
+        },
+        "estraverse": {
+          "version": "1.9.3",
+          "resolved": "https://registry.npmjs.org/estraverse/-/estraverse-1.9.3.tgz",
+          "integrity": "sha1-r2fy3JIlgkFZUJJgkaQAXSnJu0Q=",
+          "dev": true
+        },
+        "source-map": {
+          "version": "0.2.0",
+          "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.2.0.tgz",
+          "integrity": "sha1-2rc/vPwrqBm03gO9b26qSBZLP50=",
+          "dev": true,
+          "optional": true,
+          "requires": {
+            "amdefine": ">=0.0.4"
+          }
+        }
+      }
+    },
     "eslint-scope": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/eslint-scope/-/eslint-scope-4.0.0.tgz",
@@ -4899,6 +5014,12 @@
       "integrity": "sha1-1RQsDK7msRifh9OnYREGT4bIu/I=",
       "dev": true
     },
+    "fast-levenshtein": {
+      "version": "2.0.6",
+      "resolved": "https://registry.npmjs.org/fast-levenshtein/-/fast-levenshtein-2.0.6.tgz",
+      "integrity": "sha1-PYpcZog6FqMMqGQ+hR8Zuqd5eRc=",
+      "dev": true
+    },
     "fastparse": {
       "version": "1.1.1",
       "resolved": "https://registry.npmjs.org/fastparse/-/fastparse-1.1.1.tgz",
@@ -5929,6 +6050,35 @@
       "integrity": "sha1-/Xqtcmvxpf0W38KbL3pmAdJxOcQ=",
       "dev": true
     },
+    "handlebars": {
+      "version": "4.0.12",
+      "resolved": "https://registry.npmjs.org/handlebars/-/handlebars-4.0.12.tgz",
+      "integrity": "sha512-RhmTekP+FZL+XNhwS1Wf+bTTZpdLougwt5pcgA1tuz6Jcx0fpH/7z0qd71RKnZHBCxIRBHfBOnio4gViPemNzA==",
+      "dev": true,
+      "requires": {
+        "async": "^2.5.0",
+        "optimist": "^0.6.1",
+        "source-map": "^0.6.1",
+        "uglify-js": "^3.1.4"
+      },
+      "dependencies": {
+        "async": {
+          "version": "2.6.1",
+          "resolved": "https://registry.npmjs.org/async/-/async-2.6.1.tgz",
+          "integrity": "sha512-fNEiL2+AZt6AlAw/29Cr0UDe4sRAHCpEHh54WMz+Bb7QfNcFw4h3loofyJpLeQs4Yx7yuqu/2dLgM5hKOs6HlQ==",
+          "dev": true,
+          "requires": {
+            "lodash": "^4.17.10"
+          }
+        },
+        "source-map": {
+          "version": "0.6.1",
+          "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.6.1.tgz",
+          "integrity": "sha512-UjgapumWlbMhkBgzT7Ykc5YXUT46F0iKu8SGXq0bcwP5dz/h0Plj6enJqjz1Zbq2l5WaqYnrVbwWOWMyF3F47g==",
+          "dev": true
+        }
+      }
+    },
     "har-schema": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/har-schema/-/har-schema-2.0.0.tgz",
@@ -7034,6 +7184,232 @@
       "integrity": "sha1-R+Y/evVa+m+S4VAOaQ64uFKcCZo=",
       "dev": true
     },
+    "istanbul": {
+      "version": "0.4.5",
+      "resolved": "https://registry.npmjs.org/istanbul/-/istanbul-0.4.5.tgz",
+      "integrity": "sha1-ZcfXPUxNqE1POsMQuRj7C4Azczs=",
+      "dev": true,
+      "requires": {
+        "abbrev": "1.0.x",
+        "async": "1.x",
+        "escodegen": "1.8.x",
+        "esprima": "2.7.x",
+        "glob": "^5.0.15",
+        "handlebars": "^4.0.1",
+        "js-yaml": "3.x",
+        "mkdirp": "0.5.x",
+        "nopt": "3.x",
+        "once": "1.x",
+        "resolve": "1.1.x",
+        "supports-color": "^3.1.0",
+        "which": "^1.1.1",
+        "wordwrap": "^1.0.0"
+      },
+      "dependencies": {
+        "abbrev": {
+          "version": "1.0.9",
+          "resolved": "https://registry.npmjs.org/abbrev/-/abbrev-1.0.9.tgz",
+          "integrity": "sha1-kbR5JYinc4wl813W9jdSovh3YTU=",
+          "dev": true
+        },
+        "esprima": {
+          "version": "2.7.3",
+          "resolved": "https://registry.npmjs.org/esprima/-/esprima-2.7.3.tgz",
+          "integrity": "sha1-luO3DVd59q1JzQMmc9HDEnZ7pYE=",
+          "dev": true
+        },
+        "glob": {
+          "version": "5.0.15",
+          "resolved": "https://registry.npmjs.org/glob/-/glob-5.0.15.tgz",
+          "integrity": "sha1-G8k2ueAvSmA/zCIuz3Yz0wuLk7E=",
+          "dev": true,
+          "requires": {
+            "inflight": "^1.0.4",
+            "inherits": "2",
+            "minimatch": "2 || 3",
+            "once": "^1.3.0",
+            "path-is-absolute": "^1.0.0"
+          }
+        },
+        "has-flag": {
+          "version": "1.0.0",
+          "resolved": "https://registry.npmjs.org/has-flag/-/has-flag-1.0.0.tgz",
+          "integrity": "sha1-nZ55MWXOAXoA8AQYxD+UKnsdEfo=",
+          "dev": true
+        },
+        "resolve": {
+          "version": "1.1.7",
+          "resolved": "https://registry.npmjs.org/resolve/-/resolve-1.1.7.tgz",
+          "integrity": "sha1-IDEU2CrSxe2ejgQRs5ModeiJ6Xs=",
+          "dev": true
+        },
+        "supports-color": {
+          "version": "3.2.3",
+          "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-3.2.3.tgz",
+          "integrity": "sha1-ZawFBLOVQXHYpklGsq48u4pfVPY=",
+          "dev": true,
+          "requires": {
+            "has-flag": "^1.0.0"
+          }
+        },
+        "wordwrap": {
+          "version": "1.0.0",
+          "resolved": "https://registry.npmjs.org/wordwrap/-/wordwrap-1.0.0.tgz",
+          "integrity": "sha1-J1hIEIkUVqQXHI0CJkQa3pDLyus=",
+          "dev": true
+        }
+      }
+    },
+    "istanbul-lib-coverage": {
+      "version": "2.0.1",
+      "resolved": "https://registry.npmjs.org/istanbul-lib-coverage/-/istanbul-lib-coverage-2.0.1.tgz",
+      "integrity": "sha512-nPvSZsVlbG9aLhZYaC3Oi1gT/tpyo3Yt5fNyf6NmcKIayz4VV/txxJFFKAK/gU4dcNn8ehsanBbVHVl0+amOLA==",
+      "dev": true
+    },
+    "istanbul-lib-instrument": {
+      "version": "2.3.2",
+      "resolved": "https://registry.npmjs.org/istanbul-lib-instrument/-/istanbul-lib-instrument-2.3.2.tgz",
+      "integrity": "sha512-l7TD/VnBsIB2OJvSyxaLW/ab1+92dxZNH9wLH7uHPPioy3JZ8tnx2UXUdKmdkgmP2EFPzg64CToUP6dAS3U32Q==",
+      "dev": true,
+      "requires": {
+        "@babel/generator": "7.0.0-beta.51",
+        "@babel/parser": "7.0.0-beta.51",
+        "@babel/template": "7.0.0-beta.51",
+        "@babel/traverse": "7.0.0-beta.51",
+        "@babel/types": "7.0.0-beta.51",
+        "istanbul-lib-coverage": "^2.0.1",
+        "semver": "^5.5.0"
+      },
+      "dependencies": {
+        "@babel/code-frame": {
+          "version": "7.0.0-beta.51",
+          "resolved": "https://registry.npmjs.org/@babel/code-frame/-/code-frame-7.0.0-beta.51.tgz",
+          "integrity": "sha1-vXHZsZKvl435FYKdOdQJRFZDmgw=",
+          "dev": true,
+          "requires": {
+            "@babel/highlight": "7.0.0-beta.51"
+          }
+        },
+        "@babel/generator": {
+          "version": "7.0.0-beta.51",
+          "resolved": "https://registry.npmjs.org/@babel/generator/-/generator-7.0.0-beta.51.tgz",
+          "integrity": "sha1-bHV1/952HQdIXgS67cA5LG2eMPY=",
+          "dev": true,
+          "requires": {
+            "@babel/types": "7.0.0-beta.51",
+            "jsesc": "^2.5.1",
+            "lodash": "^4.17.5",
+            "source-map": "^0.5.0",
+            "trim-right": "^1.0.1"
+          }
+        },
+        "@babel/helper-function-name": {
+          "version": "7.0.0-beta.51",
+          "resolved": "https://registry.npmjs.org/@babel/helper-function-name/-/helper-function-name-7.0.0-beta.51.tgz",
+          "integrity": "sha1-IbSHSiJ8+Z7K/MMKkDAtpaJkBWE=",
+          "dev": true,
+          "requires": {
+            "@babel/helper-get-function-arity": "7.0.0-beta.51",
+            "@babel/template": "7.0.0-beta.51",
+            "@babel/types": "7.0.0-beta.51"
+          }
+        },
+        "@babel/helper-get-function-arity": {
+          "version": "7.0.0-beta.51",
+          "resolved": "https://registry.npmjs.org/@babel/helper-get-function-arity/-/helper-get-function-arity-7.0.0-beta.51.tgz",
+          "integrity": "sha1-MoGy0EWvlcFyzpGyCCXYXqRnZBE=",
+          "dev": true,
+          "requires": {
+            "@babel/types": "7.0.0-beta.51"
+          }
+        },
+        "@babel/helper-split-export-declaration": {
+          "version": "7.0.0-beta.51",
+          "resolved": "https://registry.npmjs.org/@babel/helper-split-export-declaration/-/helper-split-export-declaration-7.0.0-beta.51.tgz",
+          "integrity": "sha1-imw/ZsTSZTUvwHdIT59ugKUauXg=",
+          "dev": true,
+          "requires": {
+            "@babel/types": "7.0.0-beta.51"
+          }
+        },
+        "@babel/highlight": {
+          "version": "7.0.0-beta.51",
+          "resolved": "https://registry.npmjs.org/@babel/highlight/-/highlight-7.0.0-beta.51.tgz",
+          "integrity": "sha1-6IRK4loVlcz9QriWI7Q3bKBtIl0=",
+          "dev": true,
+          "requires": {
+            "chalk": "^2.0.0",
+            "esutils": "^2.0.2",
+            "js-tokens": "^3.0.0"
+          }
+        },
+        "@babel/parser": {
+          "version": "7.0.0-beta.51",
+          "resolved": "https://registry.npmjs.org/@babel/parser/-/parser-7.0.0-beta.51.tgz",
+          "integrity": "sha1-J87C30Cd9gr1gnDtj2qlVAnqhvY=",
+          "dev": true
+        },
+        "@babel/template": {
+          "version": "7.0.0-beta.51",
+          "resolved": "https://registry.npmjs.org/@babel/template/-/template-7.0.0-beta.51.tgz",
+          "integrity": "sha1-lgKkCuvPNXrpZ34lMu9fyBD1+/8=",
+          "dev": true,
+          "requires": {
+            "@babel/code-frame": "7.0.0-beta.51",
+            "@babel/parser": "7.0.0-beta.51",
+            "@babel/types": "7.0.0-beta.51",
+            "lodash": "^4.17.5"
+          }
+        },
+        "@babel/traverse": {
+          "version": "7.0.0-beta.51",
+          "resolved": "https://registry.npmjs.org/@babel/traverse/-/traverse-7.0.0-beta.51.tgz",
+          "integrity": "sha1-mB2vLOw0emIx06odnhgDsDqqpKg=",
+          "dev": true,
+          "requires": {
+            "@babel/code-frame": "7.0.0-beta.51",
+            "@babel/generator": "7.0.0-beta.51",
+            "@babel/helper-function-name": "7.0.0-beta.51",
+            "@babel/helper-split-export-declaration": "7.0.0-beta.51",
+            "@babel/parser": "7.0.0-beta.51",
+            "@babel/types": "7.0.0-beta.51",
+            "debug": "^3.1.0",
+            "globals": "^11.1.0",
+            "invariant": "^2.2.0",
+            "lodash": "^4.17.5"
+          }
+        },
+        "@babel/types": {
+          "version": "7.0.0-beta.51",
+          "resolved": "https://registry.npmjs.org/@babel/types/-/types-7.0.0-beta.51.tgz",
+          "integrity": "sha1-2AK3tUO1g2x3iqaReXq/APPZfqk=",
+          "dev": true,
+          "requires": {
+            "esutils": "^2.0.2",
+            "lodash": "^4.17.5",
+            "to-fast-properties": "^2.0.0"
+          }
+        },
+        "globals": {
+          "version": "11.7.0",
+          "resolved": "https://registry.npmjs.org/globals/-/globals-11.7.0.tgz",
+          "integrity": "sha512-K8BNSPySfeShBQXsahYB/AbbWruVOTyVpgoIDnl8odPpeSfP2J5QO2oLFFdl2j7GfDCtZj2bMKar2T49itTPCg==",
+          "dev": true
+        },
+        "jsesc": {
+          "version": "2.5.1",
+          "resolved": "https://registry.npmjs.org/jsesc/-/jsesc-2.5.1.tgz",
+          "integrity": "sha1-5CGiqOINawgZ3yiQj3glJrlt0f4=",
+          "dev": true
+        },
+        "to-fast-properties": {
+          "version": "2.0.0",
+          "resolved": "https://registry.npmjs.org/to-fast-properties/-/to-fast-properties-2.0.0.tgz",
+          "integrity": "sha1-3F5pjL0HkmW8c+A3doGk5Og/YW4=",
+          "dev": true
+        }
+      }
+    },
     "js-base64": {
       "version": "2.4.8",
       "resolved": "https://registry.npmjs.org/js-base64/-/js-base64-2.4.8.tgz",
@@ -7208,6 +7584,19 @@
         "which": "^1.2.1"
       }
     },
+    "karma-coverage": {
+      "version": "1.1.2",
+      "resolved": "https://registry.npmjs.org/karma-coverage/-/karma-coverage-1.1.2.tgz",
+      "integrity": "sha512-eQawj4Cl3z/CjxslYy9ariU4uDh7cCNFZHNWXWRpl0pNeblY/4wHR7M7boTYXWrn9bY0z2pZmr11eKje/S/hIw==",
+      "dev": true,
+      "requires": {
+        "dateformat": "^1.0.6",
+        "istanbul": "^0.4.0",
+        "lodash": "^4.17.0",
+        "minimatch": "^3.0.0",
+        "source-map": "^0.5.1"
+      }
+    },
     "karma-mocha": {
       "version": "1.3.0",
       "resolved": "https://registry.npmjs.org/karma-mocha/-/karma-mocha-1.3.0.tgz",
@@ -7327,6 +7716,16 @@
         "invert-kv": "^1.0.0"
       }
     },
+    "levn": {
+      "version": "0.3.0",
+      "resolved": "https://registry.npmjs.org/levn/-/levn-0.3.0.tgz",
+      "integrity": "sha1-OwmSTt+fCDwEkP3UwLxEIeBHZO4=",
+      "dev": true,
+      "requires": {
+        "prelude-ls": "~1.1.2",
+        "type-check": "~0.3.2"
+      }
+    },
     "load-json-file": {
       "version": "1.1.0",
       "resolved": "https://registry.npmjs.org/load-json-file/-/load-json-file-1.1.0.tgz",
@@ -8383,6 +8782,28 @@
         "last-call-webpack-plugin": "^3.0.0"
       }
     },
+    "optionator": {
+      "version": "0.8.2",
+      "resolved": "https://registry.npmjs.org/optionator/-/optionator-0.8.2.tgz",
+      "integrity": "sha1-NkxeQJ0/TWMB1sC0wFu6UBgK62Q=",
+      "dev": true,
+      "requires": {
+        "deep-is": "~0.1.3",
+        "fast-levenshtein": "~2.0.4",
+        "levn": "~0.3.0",
+        "prelude-ls": "~1.1.2",
+        "type-check": "~0.3.2",
+        "wordwrap": "~1.0.0"
+      },
+      "dependencies": {
+        "wordwrap": {
+          "version": "1.0.0",
+          "resolved": "https://registry.npmjs.org/wordwrap/-/wordwrap-1.0.0.tgz",
+          "integrity": "sha1-J1hIEIkUVqQXHI0CJkQa3pDLyus=",
+          "dev": true
+        }
+      }
+    },
     "original": {
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/original/-/original-1.0.2.tgz",
@@ -9949,6 +10370,12 @@
       "integrity": "sha1-h/OPnxj3dKSrTIojL1xc6IcqnRU=",
       "dev": true
     },
+    "prelude-ls": {
+      "version": "1.1.2",
+      "resolved": "https://registry.npmjs.org/prelude-ls/-/prelude-ls-1.1.2.tgz",
+      "integrity": "sha1-IZMqVJ9eUv/ZqCf1cOBL5iqX2lQ=",
+      "dev": true
+    },
     "preserve": {
       "version": "0.2.0",
       "resolved": "https://registry.npmjs.org/preserve/-/preserve-0.2.0.tgz",
@@ -11988,6 +12415,121 @@
         "inherits": "2"
       }
     },
+    "test-exclude": {
+      "version": "5.0.0",
+      "resolved": "https://registry.npmjs.org/test-exclude/-/test-exclude-5.0.0.tgz",
+      "integrity": "sha512-bO3Lj5+qFa9YLfYW2ZcXMOV1pmQvw+KS/DpjqhyX6Y6UZ8zstpZJ+mA2ERkXfpOqhxsJlQiLeVXD3Smsrs6oLw==",
+      "dev": true,
+      "requires": {
+        "arrify": "^1.0.1",
+        "minimatch": "^3.0.4",
+        "read-pkg-up": "^4.0.0",
+        "require-main-filename": "^1.0.1"
+      },
+      "dependencies": {
+        "find-up": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/find-up/-/find-up-3.0.0.tgz",
+          "integrity": "sha512-1yD6RmLI1XBfxugvORwlck6f75tYL+iR0jqwsOrOxMZyGYqUuDhJ0l4AXdO1iX/FTs9cBAMEk1gWSEx1kSbylg==",
+          "dev": true,
+          "requires": {
+            "locate-path": "^3.0.0"
+          }
+        },
+        "load-json-file": {
+          "version": "4.0.0",
+          "resolved": "https://registry.npmjs.org/load-json-file/-/load-json-file-4.0.0.tgz",
+          "integrity": "sha1-L19Fq5HjMhYjT9U62rZo607AmTs=",
+          "dev": true,
+          "requires": {
+            "graceful-fs": "^4.1.2",
+            "parse-json": "^4.0.0",
+            "pify": "^3.0.0",
+            "strip-bom": "^3.0.0"
+          }
+        },
+        "locate-path": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/locate-path/-/locate-path-3.0.0.tgz",
+          "integrity": "sha512-7AO748wWnIhNqAuaty2ZWHkQHRSNfPVIsPIfwEOWO22AmaoVrWavlOcMR5nzTLNYvp36X220/maaRsrec1G65A==",
+          "dev": true,
+          "requires": {
+            "p-locate": "^3.0.0",
+            "path-exists": "^3.0.0"
+          }
+        },
+        "p-limit": {
+          "version": "2.0.0",
+          "resolved": "https://registry.npmjs.org/p-limit/-/p-limit-2.0.0.tgz",
+          "integrity": "sha512-fl5s52lI5ahKCernzzIyAP0QAZbGIovtVHGwpcu1Jr/EpzLVDI2myISHwGqK7m8uQFugVWSrbxH7XnhGtvEc+A==",
+          "dev": true,
+          "requires": {
+            "p-try": "^2.0.0"
+          }
+        },
+        "p-locate": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/p-locate/-/p-locate-3.0.0.tgz",
+          "integrity": "sha512-x+12w/To+4GFfgJhBEpiDcLozRJGegY+Ei7/z0tSLkMmxGZNybVMSfWj9aJn8Z5Fc7dBUNJOOVgPv2H7IwulSQ==",
+          "dev": true,
+          "requires": {
+            "p-limit": "^2.0.0"
+          }
+        },
+        "p-try": {
+          "version": "2.0.0",
+          "resolved": "https://registry.npmjs.org/p-try/-/p-try-2.0.0.tgz",
+          "integrity": "sha512-hMp0onDKIajHfIkdRk3P4CdCmErkYAxxDtP3Wx/4nZ3aGlau2VKh3mZpcuFkH27WQkL/3WBCPOktzA9ZOAnMQQ==",
+          "dev": true
+        },
+        "parse-json": {
+          "version": "4.0.0",
+          "resolved": "https://registry.npmjs.org/parse-json/-/parse-json-4.0.0.tgz",
+          "integrity": "sha1-vjX1Qlvh9/bHRxhPmKeIy5lHfuA=",
+          "dev": true,
+          "requires": {
+            "error-ex": "^1.3.1",
+            "json-parse-better-errors": "^1.0.1"
+          }
+        },
+        "path-type": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/path-type/-/path-type-3.0.0.tgz",
+          "integrity": "sha512-T2ZUsdZFHgA3u4e5PfPbjd7HDDpxPnQb5jN0SrDsjNSuVXHJqtwTnWqG0B1jZrgmJ/7lj1EmVIByWt1gxGkWvg==",
+          "dev": true,
+          "requires": {
+            "pify": "^3.0.0"
+          }
+        },
+        "read-pkg": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/read-pkg/-/read-pkg-3.0.0.tgz",
+          "integrity": "sha1-nLxoaXj+5l0WwA4rGcI3/Pbjg4k=",
+          "dev": true,
+          "requires": {
+            "load-json-file": "^4.0.0",
+            "normalize-package-data": "^2.3.2",
+            "path-type": "^3.0.0"
+          }
+        },
+        "read-pkg-up": {
+          "version": "4.0.0",
+          "resolved": "https://registry.npmjs.org/read-pkg-up/-/read-pkg-up-4.0.0.tgz",
+          "integrity": "sha512-6etQSH7nJGsK0RbG/2TeDzZFa8shjQ1um+SwQQ5cwKy0dhSXdOncEhb1CPpvQG4h7FyOV6EB6YlV0yJvZQNAkA==",
+          "dev": true,
+          "requires": {
+            "find-up": "^3.0.0",
+            "read-pkg": "^3.0.0"
+          }
+        },
+        "strip-bom": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/strip-bom/-/strip-bom-3.0.0.tgz",
+          "integrity": "sha1-IzTBjpx1n3vdVv3vfprj1YjmjtM=",
+          "dev": true
+        }
+      }
+    },
     "text-table": {
       "version": "0.2.0",
       "resolved": "https://registry.npmjs.org/text-table/-/text-table-0.2.0.tgz",
@@ -12187,6 +12729,15 @@
       "dev": true,
       "optional": true
     },
+    "type-check": {
+      "version": "0.3.2",
+      "resolved": "https://registry.npmjs.org/type-check/-/type-check-0.3.2.tgz",
+      "integrity": "sha1-WITKtRLPHTVeP7eE8wgEsrUg23I=",
+      "dev": true,
+      "requires": {
+        "prelude-ls": "~1.1.2"
+      }
+    },
     "type-is": {
       "version": "1.6.16",
       "resolved": "https://registry.npmjs.org/type-is/-/type-is-1.6.16.tgz",
diff --git a/package.json b/package.json
index 3171fa5..4f672db 100644
--- a/package.json
+++ b/package.json
@@ -4,11 +4,11 @@
   "description": "",
   "main": "index.js",
   "scripts": {
-    "build": "webpack --env production",
+    "build": "webpack --mode production",
     "build:i18n": "webpack --config webpack.i18n.js",
     "build:ssr": "webpack --config webpack.ssr.js",
-    "build:stats": "webpack --env production --json > stats.json",
-    "start": "webpack-dev-server --env development",
+    "build:stats": "webpack --mode production --json > stats.json",
+    "start": "webpack-dev-server --mode development",
     "test": "echo \"Error: no test specified\" && exit 1",
     "test:karma": "karma start",
     "test:karma:watch": "karma start --auto-watch --no-single-run",
@@ -24,6 +24,7 @@
     "@babel/preset-react": "^7.0.0",
     "autoprefixer": "^9.1.5",
     "babel-loader": "^8.0.4",
+    "babel-plugin-istanbul": "^5.0.1",
     "babel-plugin-syntax-dynamic-import": "^6.18.0",
     "babel-preset-env": "^1.7.0",
     "babel-preset-react": "^6.24.1",
@@ -39,6 +40,7 @@
     "i18n-webpack-plugin": "^1.0.0",
     "karma": "^3.0.0",
     "karma-chrome-launcher": "^2.2.0",
+    "karma-coverage": "^1.1.2",
     "karma-mocha": "^1.3.0",
     "karma-webpack": "^3.0.5",
     "mini-css-extract-plugin": "^0.4.1",