add test coverage

package.json

@@ -29,6 +29,7 @@
     "build": "rollup -c && yarn build:types",
     "build:types": "tsc",
     "test": "react-scripts test",
+    "test:coverage": "yarn test --coverage --watchAll=false ",
     "eject": "react-scripts eject",
     "storybook": "start-storybook -p 6006 -s public",
     "build-storybook": "build-storybook -s public"
@@ -99,5 +100,23 @@
   "homepage": "https://github.com/vegaprotocol/ui-toolkit",
   "keywords": [
     "vega"
-  ]
+  ],
+  "jest": {
+    "collectCoverageFrom": [
+      "**/**/*.{ts,tsx}",
+      "!**/**/*.stories.tsx"
+    ],
+    "coverageReporters": [
+      "html",
+      "json"
+    ],
+    "coverageThreshold": {
+      "global": {
+        "branches": 100,
+        "functions": 100,
+        "lines": 100,
+        "statements": 100
+      }
+    }
+  }
 }

src/components/etherscan-link/etherscan-link.test.tsx

@@ -41,3 +41,25 @@ test("It links to ropsten etherscan if network is ropsten", () => {
     "https://ropsten.etherscan.io/address/address"
   );
 });
+
+test("Doesn't render for address if chainid is null", () => {
+  render(<EtherscanLink chainId={null} address="address" />);
+  expect(screen.queryByTestId("etherscan-link")).not.toBeInTheDocument();
+});
+
+test("Doesn't render for tx if chainid is null", () => {
+  render(<EtherscanLink chainId={null} tx="tx" />);
+  expect(screen.queryByTestId("etherscan-link")).not.toBeInTheDocument();
+});
+
+test("Doesn't render for address if chainid is unknown", () => {
+  // @ts-ignore
+  render(<EtherscanLink chainId={"foo"} address="address" />);
+  expect(screen.queryByTestId("etherscan-link")).not.toBeInTheDocument();
+});
+
+test("Doesn't render for tx if chainid is unknown", () => {
+  // @ts-ignore
+  render(<EtherscanLink chainId={"foo"} tx="tx" />);
+  expect(screen.queryByTestId("etherscan-link")).not.toBeInTheDocument();
+});