diff --git a/bsconfig.json b/bsconfig.json
index 7caafba..fed06d3 100644
--- a/bsconfig.json
+++ b/bsconfig.json
@@ -7,12 +7,17 @@
   "bs-dev-dependencies": [
     "@glennsl/bs-jest",
     "bs-jest-dom",
-    "bs-react-testing-library"
+    "bs-react-testing-library",
+    "bs-webapi"
   ],
   "sources": [
     {
       "dir": "src",
       "subdirs": [
+        {
+          "dir": "__tests__",
+          "type": "dev"
+        },
         {
           "dir": "components",
           "subdirs": [
@@ -26,7 +31,7 @@
     }
   ],
   "package-specs": {
-    "module": "es6",
+    "module": "commonjs",
     "in-source": true
   },
   "suffix": ".bs.js",
diff --git a/package.json b/package.json
index 4edfe56..57db688 100644
--- a/package.json
+++ b/package.json
@@ -32,9 +32,10 @@
     "@glennsl/bs-jest": "^0.4.8",
     "@wyze/changelog": "^1.0.0",
     "@wyze/github-release": "^1.0.0",
-    "bs-jest-dom": "^2.0.0",
+    "bs-jest-dom": "^2.0.1",
     "bs-platform": "^5.0.3",
-    "bs-react-testing-library": "^0.4.0",
+    "bs-react-testing-library": "^0.5.0",
+    "bs-webapi": "^0.14.2",
     "bsb-js": "^1.1.7",
     "npm-run-all": "^4.1.5",
     "parcel-bundler": "^1.12.3",
diff --git a/src/__tests__/store_test.re b/src/__tests__/store_test.re
new file mode 100644
index 0000000..2db956c
--- /dev/null
+++ b/src/__tests__/store_test.re
@@ -0,0 +1,274 @@
+open Jest;
+open Expect;
+open Store;
+
+let run = actions =>
+  actions
+  |> List.fold_left((state, action) => reducer(state, action), [])
+  |> List.map(({action, left, right, total}) =>
+       (left, right, action, total)
+     );
+
+test("reducer handles Clear action", () => {
+  let actual = [Input("1"), Add, Input("3"), Clear]->run;
+  let expected = [];
+
+  expect(actual) |> toEqual(expected);
+});
+
+test("reducer handles Equals action", () => {
+  let actual = [Input("1"), Add, Input("2"), Equals]->run;
+  let expected = [("3", "3", Equals, 3.), ("1", "2", Add, 3.)];
+
+  expect(actual) |> toEqual(expected);
+});
+
+test("reducer handles double Equals action", () => {
+  let actual = [Input("1"), Add, Input("2"), Equals, Equals]->run;
+  let expected = [
+    ("5", "5", Equals, 5.),
+    ("3", "2", Add, 5.),
+    ("3", "3", Equals, 3.),
+    ("1", "2", Add, 3.),
+  ];
+
+  expect(actual) |> toEqual(expected);
+});
+
+test("reducer handles Input action with no previous state", () => {
+  let actual = [Input("4")]->run;
+  let expected = [("4", "", Pending, 4.)];
+
+  expect(actual) |> toEqual(expected);
+});
+
+test("reducer handles Input action with Pending state", () => {
+  let actual = [Input("1"), Input("4")]->run;
+  let expected = [("14", "", Pending, 14.)];
+
+  expect(actual) |> toEqual(expected);
+});
+
+test("reducer handles Input action with non-Pending state", () => {
+  let actual = [Input("1"), Add, Input("4")]->run;
+  let expected = [("1", "4", Add, 5.)];
+
+  expect(actual) |> toEqual(expected);
+});
+
+test("reducer handles Input action after Equals state", () => {
+  let actual = [Input("1"), Add, Input("2"), Equals, Input("4")]->run;
+  let expected = [
+    ("4", "", Pending, 4.),
+    ("3", "3", Equals, 3.),
+    ("1", "2", Add, 3.),
+  ];
+
+  expect(actual) |> toEqual(expected);
+});
+
+test("reducer handles Add action", () => {
+  let actual = [Input("1"), Add]->run;
+  let expected = [("1", "", Add, 1.)];
+
+  expect(actual) |> toEqual(expected);
+});
+
+test("reducer handles switch from Add to Subtract action", () => {
+  let actual = [Input("1"), Add, Subtract]->run;
+  let expected = [("1", "", Subtract, 1.)];
+
+  expect(actual) |> toEqual(expected);
+});
+
+test("reducer handles Add action after Equals action", () => {
+  let actual = [Input("1"), Add, Input("1"), Equals, Add]->run;
+  let expected = [
+    ("2", "", Add, 2.),
+    ("2", "2", Equals, 2.),
+    ("1", "1", Add, 2.),
+  ];
+
+  expect(actual) |> toEqual(expected);
+});
+
+describe("PosNeg", () => {
+  test("with initial state", () => {
+    let actual = [PosNeg]->run;
+    let expected = [];
+
+    expect(actual) |> toEqual(expected);
+  });
+
+  test("with Pending state", () => {
+    let actual = [Input("4"), PosNeg]->run;
+    let expected = [("-4", "", Pending, (-4.))];
+
+    expect(actual) |> toEqual(expected);
+  });
+
+  test("when total would be 0", () => {
+    let actual = [Input("5"), Subtract, Input("5"), PosNeg]->run;
+    let expected = [("5", "-5", Subtract, 10.)];
+
+    expect(actual) |> toEqual(expected);
+  });
+
+  test("with no right value", () => {
+    let actual = [Input("4"), Add, PosNeg]->run;
+    let expected = [("4", "-4", Add, 0.)];
+
+    expect(actual) |> toEqual(expected);
+  });
+
+  test("with non-Pending state", () => {
+    let actual = [Input("4"), Add, Input("2"), PosNeg]->run;
+    let expected = [("4", "-2", Add, 2.)];
+
+    expect(actual) |> toEqual(expected);
+  });
+
+  test("handles sequence: PosNeg -> Equals -> Equals", () => {
+    let actual =
+      [Input("5"), Multiply, Input("3"), PosNeg, Equals, Equals]->run;
+    let expected = [
+      ("45", "45", Equals, 45.),
+      ("-15", "-3", Multiply, 45.),
+      ("-15", "-15", Equals, (-15.)),
+      ("5", "-3", Multiply, (-15.)),
+    ];
+
+    expect(actual) |> toEqual(expected);
+  });
+
+  test("handles sequence: Equals -> PosNeg -> Equals", () => {
+    let actual =
+      [Input("5"), Multiply, Input("3"), PosNeg, Equals, PosNeg, Equals]
+      ->run;
+    let expected = [
+      ("-45", "-45", Equals, (-45.)),
+      ("15", "-3", Multiply, (-45.)),
+      ("15", "15", Equals, 15.),
+      ("5", "-3", Multiply, (-15.)),
+    ];
+
+    expect(actual) |> toEqual(expected);
+  });
+});
+
+test("reducer handles decimals", () => {
+  let actual =
+    [
+      Input("5"),
+      Input("."),
+      Input("3"),
+      Add,
+      Input("4"),
+      Input("."),
+      Input("7"),
+      Equals,
+    ]
+    ->run;
+  let expected = [("10", "10", Equals, 10.), ("5.3", "4.7", Add, 10.)];
+
+  expect(actual) |> toEqual(expected);
+});
+
+test("reducer handles double decimals", () => {
+  let actual =
+    [
+      Input("2"),
+      Input("."),
+      Input("."),
+      Input("3"),
+      Add,
+      Input("2"),
+      Input("."),
+      Input("7"),
+      Input("."),
+      Input("5"),
+      Equals,
+    ]
+    ->run;
+  let expected = [
+    ("5.05", "5.05", Equals, 5.05),
+    ("2.3", "2.75", Add, 5.05),
+  ];
+
+  expect(actual) |> toEqual(expected);
+});
+
+describe("Percent", () => {
+  test("with initial state", () => {
+    let actual = [Percent]->run;
+    let expected = [];
+
+    expect(actual) |> toEqual(expected);
+  });
+
+  test("with Pending state", () => {
+    let actual = [Input("4"), Percent]->run;
+    let expected = [("0.04", "", Pending, 0.04)];
+
+    expect(actual) |> toEqual(expected);
+  });
+
+  test("with no right value", () => {
+    let actual = [Input("4"), Add, Percent]->run;
+    let expected = [("4", "0.04", Add, 4.04)];
+
+    expect(actual) |> toEqual(expected);
+  });
+
+  test("with non-Pending state", () => {
+    let actual = [Input("4"), Add, Input("2"), Percent]->run;
+    let expected = [("4", "0.02", Add, 4.02)];
+
+    expect(actual) |> toEqual(expected);
+  });
+
+  test("handles sequence: Percent -> Equals -> Equals", () => {
+    let actual =
+      [
+        Input("5"),
+        Multiply,
+        Input("5"),
+        Input("0"),
+        Percent,
+        Equals,
+        Equals,
+      ]
+      ->run;
+    let expected = [
+      ("1.25", "1.25", Equals, 1.25),
+      ("2.5", "0.5", Multiply, 1.25),
+      ("2.5", "2.5", Equals, 2.5),
+      ("5", "0.5", Multiply, 2.5),
+    ];
+
+    expect(actual) |> toEqual(expected);
+  });
+
+  test("handles sequence: Equals -> Percent -> Equals", () => {
+    let actual =
+      [
+        Input("5"),
+        Multiply,
+        Input("5"),
+        Input("0"),
+        Percent,
+        Equals,
+        Percent,
+        Equals,
+      ]
+      ->run;
+    let expected = [
+      ("0.0125", "0.0125", Equals, 0.0125),
+      ("0.025", "0.5", Multiply, 0.0125),
+      ("0.025", "0.025", Equals, 0.025),
+      ("5", "0.5", Multiply, 2.5),
+    ];
+
+    expect(actual) |> toEqual(expected);
+  });
+});
diff --git a/src/components/App.re b/src/components/App.re
index e7c5ded..1d73d0b 100644
--- a/src/components/App.re
+++ b/src/components/App.re
@@ -49,7 +49,10 @@ let make = () => {
   <div className=Styles.container>
     <Hero />
     <div className=Styles.calculator>
-      <div className=Styles.display> display->React.string </div>
+      <label className=Styles.display>
+        display->React.string
+        <input type_="hidden" />
+      </label>
       <div className=Styles.buttons>
         <Button action=Clear text="C" />
         <Button action=PosNeg text={js|+/\u2212|js} />
diff --git a/src/components/Checkmark.re b/src/components/Checkmark.re
index c7460e9..6c87d09 100644
--- a/src/components/Checkmark.re
+++ b/src/components/Checkmark.re
@@ -1,6 +1,6 @@
 [@react.component]
 let make = () =>
-  <Svg>
+  <Svg title="checkmark">
     <circle cx="32" cy="32" r="30" fill="#4bd37b" />
     <path fill="#fff" d="m46 14l-21 21.6-7-7.2-7 7.2 14 14.4 28-28.8z" />
   </Svg>;
diff --git a/src/components/Soon.re b/src/components/Soon.re
index 5426b8d..3ed9142 100644
--- a/src/components/Soon.re
+++ b/src/components/Soon.re
@@ -1,6 +1,6 @@
 [@react.component]
 let make = () =>
-  <Svg>
+  <Svg title="soon">
     <g fill="#4d5357">
       <path d="m61 18l-16-16v10h-42v12h42v10z" />
       <path
diff --git a/src/components/Svg.re b/src/components/Svg.re
index 63c86e9..d599b45 100644
--- a/src/components/Svg.re
+++ b/src/components/Svg.re
@@ -2,23 +2,20 @@ module Styles = {
   open Css;
 
   let container =
-    merge([
-      style([
-        height(px(16)),
-        marginRight(em(1.)),
-        marginTop(`zero),
-        width(px(16)),
-      ]),
-      style([media("(min-width: 53.125em)", [marginTop(px(-6))])]),
+    style([
+      height(px(16)),
+      marginRight(em(1.)),
+      marginTop(`zero),
+      width(px(16)),
     ]);
 };
 
 [@react.component]
-let make = (~children) =>
-  <div className=Styles.container>
-    <svg
-      xmlns="http://www.w3.org/2000/svg"
-      viewBox="0 0 64 64">
-      <g> children </g>
-    </svg>
-  </div>;
+let make = (~children, ~title) =>
+  <svg
+    className=Styles.container
+    viewBox="0 0 64 64"
+    xmlns="http://www.w3.org/2000/svg">
+    <title> title->React.string </title>
+    <g> children </g>
+  </svg>;
diff --git a/src/components/__tests__/App_test.re b/src/components/__tests__/App_test.re
new file mode 100644
index 0000000..16a2998
--- /dev/null
+++ b/src/components/__tests__/App_test.re
@@ -0,0 +1,78 @@
+open Jest;
+open Expect;
+open JestDom;
+open ReactTestingLibrary;
+open Webapi.Dom;
+
+let unwrap = element =>
+  switch (element) {
+  | Some(el) => el
+  | None => raise(Failure("Element not found"))
+  };
+
+test("renders the title", () =>
+  <Root />
+  |> render
+  |> getByText(~matcher=`Str("Reason Calculator"))
+  |> expect
+  |> toBeInTheDocument
+);
+
+testAll(
+  "renders feature",
+  [
+    ("Simple operations", "checkmark"),
+    ("Decimals", "checkmark"),
+    ("Percentage", "checkmark"),
+    ("Positive/Negative", "checkmark"),
+    ("Advanced options", "soon"),
+    ("Operation history", "soon"),
+  ],
+  ((feature, icon)) =>
+  <Root />
+  |> render
+  |> getByText(
+       ~matcher=
+         `Func(
+           (_, el) =>
+             el->Element.parentNode->unwrap->Node.textContent == icon
+             ++ feature,
+         ),
+     )
+  |> expect
+  |> toBeInTheDocument
+);
+
+test("renders display", () => {
+  let app = <Root /> |> render;
+  let oneButton = app |> getByText(~matcher=`Str("1"));
+
+  oneButton->FireEvent.click;
+  oneButton->FireEvent.click;
+
+  app |> getByLabelText(~matcher=`Str("11")) |> expect |> toBeInTheDocument;
+});
+
+testAll(
+  "performs operation",
+  [
+    (["1", "+", "2", "="], "3"),
+    (["1", {js|\u2212|js}, "2", "="], "-1"),
+    (["2", {js|\u00d7|js}, "3", "="], "6"),
+    (["4", {js|\u00f7|js}, "2", "="], "2"),
+  ],
+  ((operations, result)) => {
+    let app = <Root /> |> render;
+
+    List.iter(
+      operation =>
+        app |> getByText(~matcher=`Str(operation)) |> FireEvent.click,
+      operations,
+    );
+
+    app
+    |> getByLabelText(~matcher=`Str(result))
+    |> expect
+    |> toBeInTheDocument;
+  },
+);
diff --git a/yarn.lock b/yarn.lock
index 46885af..bad3fd8 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1582,17 +1582,17 @@ bs-css@^8.0.4:
   dependencies:
     emotion "^9.2.12"
 
-bs-dom-testing-library@^0.3.0:
-  version "0.3.0"
-  resolved "https://registry.yarnpkg.com/bs-dom-testing-library/-/bs-dom-testing-library-0.3.0.tgz#5bef758504a6f0fa420964be072033478cfe3369"
-  integrity sha512-FDstGF2VSgADodpRq4T0gLO1L6WNDXHPlGc+92WZ/sftdzC4rzdbo0AFJNNAUPWiECt6yoK+JJXkrZtIbUfjeA==
+bs-dom-testing-library@^0.4.1:
+  version "0.4.1"
+  resolved "https://registry.yarnpkg.com/bs-dom-testing-library/-/bs-dom-testing-library-0.4.1.tgz#46fd1fea65465edd799f1e7dd1596a633ef44b05"
+  integrity sha512-UxpDl6Ain7ZvjieWFeeJZjmcaZOVe8KAKo9Olnji1kF5ne2w9x+b8AzSC0z20OKhpP3/SiiAuRnGNiO81NqI6A==
   dependencies:
-    dom-testing-library "^3.8.1"
+    dom-testing-library "^3.19.0"
 
-bs-jest-dom@^2.0.0:
-  version "2.0.0"
-  resolved "https://registry.yarnpkg.com/bs-jest-dom/-/bs-jest-dom-2.0.0.tgz#a5311326f473bd353eda77964a0c75c4666702ac"
-  integrity sha512-Q/cnUTCC1fqDGi7myFP3tVqW2YSXv0UFZmHL1qz5G4tUAW3AqqxpToIc4Jzt8pjTB4sJ7bPt5sj0cRW+1nS4HA==
+bs-jest-dom@^2.0.1:
+  version "2.0.1"
+  resolved "https://registry.yarnpkg.com/bs-jest-dom/-/bs-jest-dom-2.0.1.tgz#8aabe5a7910db4a4f9e9fb77014b8e33f61e5e13"
+  integrity sha512-BgO+oQQqa13HEuMI3xGk1WDMdZA61/8zcc6PA+gdFhz5MMYTeCMsx9pzVu9YCTPDvv1U2QpE38SU9BNUDR94kA==
   dependencies:
     "@glennsl/bs-jest" "^0.4.8"
     jest-dom "^3.1.2"
@@ -1602,14 +1602,19 @@ bs-platform@^5.0.3:
   resolved "https://registry.yarnpkg.com/bs-platform/-/bs-platform-5.0.3.tgz#2b167603ef52574cb9534fabab702f6013715e6c"
   integrity sha512-GAeypBebeDGTay5kJ3v5Z3Whp1Q4zQ0hAttflVtPG3zps88xDZnVAlS3JGIIBDmJFEMyNtv5947a/IWKvWXcPw==
 
-bs-react-testing-library@^0.4.0:
-  version "0.4.0"
-  resolved "https://registry.yarnpkg.com/bs-react-testing-library/-/bs-react-testing-library-0.4.0.tgz#096bcc12f1023290ac393d763d0a108d6d678256"
-  integrity sha512-q3dYC9/hxhe/MjuHMUZhWJ2vQ185FZobYOah7pN+RNDXUn1Kyl2STrfCI7OczGIgtICYnw8Cfa2i5N+6MDvwgQ==
+bs-react-testing-library@^0.5.0:
+  version "0.5.0"
+  resolved "https://registry.yarnpkg.com/bs-react-testing-library/-/bs-react-testing-library-0.5.0.tgz#3906666ffc6dfd22ff25ae01bfa8f5ba65c30db0"
+  integrity sha512-EmISyRVFXCipeaaymKKv34kf8Cnn40hg3oRU2E36VLvou6XznkvMtAaWqYIGupp1+cnWkFNXhQAMZJNwSd9JiA==
   dependencies:
-    bs-dom-testing-library "^0.3.0"
+    bs-dom-testing-library "^0.4.1"
     react-testing-library "^5.2.0"
 
+bs-webapi@^0.14.2:
+  version "0.14.2"
+  resolved "https://registry.yarnpkg.com/bs-webapi/-/bs-webapi-0.14.2.tgz#4f5db785b3a01c8f206816185465da5ddc2f08b2"
+  integrity sha512-EwL3Vi1972aMyUa3gjXXkTpS827QSU84RlIS32Pnhtrmu1Jv5f25cCnAagRNslOj3l/bBo0DOIpBQ481SL54eA==
+
 bsb-js@^1.1.7:
   version "1.1.7"
   resolved "https://registry.yarnpkg.com/bsb-js/-/bsb-js-1.1.7.tgz#12cc91e974f5896b3a2aa8358419d24e56f552c3"
@@ -2485,7 +2490,7 @@ dom-serializer@0:
     domelementtype "^1.3.0"
     entities "^1.1.1"
 
-dom-testing-library@^3.13.1, dom-testing-library@^3.8.1:
+dom-testing-library@^3.13.1, dom-testing-library@^3.19.0:
   version "3.19.3"
   resolved "https://registry.yarnpkg.com/dom-testing-library/-/dom-testing-library-3.19.3.tgz#fba399987be1bdd57b07c4bc3ef46c3c084b26d9"
   integrity sha512-oiI+oq91iO/Vpp+pt8PqfqLfBK074FH0eprhoFNvBCvJOk7vL4ozbe/yj/kEEGR6kiT4F3MAam19AX1fdGFjrA==