Add tests for format_text.js

This commit adds tests for format_text,
with the aim to improve the code coverage of the
whole repo.

Part of https://github.com/bigchaindb/js-bigchaindb-driver/issues/220

test/text-format/test_format_text.js

@@ -0,0 +1,48 @@
+import test from 'ava'
+import formatText from '../../src/format_text'
+
+test('formatText test type 1', t => {
+    const expected = 'Hi there Dimi!'
+    const actual = formatText('Hi there ${dimi}!', { dimi: 'Dimi' }) // eslint-disable-line no-template-curly-in-string
+
+    t.is(actual, expected)
+})
+
+test('formatText test type 2', t => {
+    const expected = 'BigchainDB is big'
+    const actual = formatText('${database} is %(status)s', { // eslint-disable-line no-template-curly-in-string
+        database: 'BigchainDB',
+        status: 'big'
+    })
+
+    t.is(actual, expected)
+})
+
+test('formatText test type 3', t => {
+    const expected = 'Berlin is best known for its Currywurst'
+    const actual = formatText(
+        'Berlin is best known for its ${berlin.topKnownFor[0].name}', // eslint-disable-line no-template-curly-in-string
+        {
+            berlin: {
+                topKnownFor: [
+                    {
+                        name: 'Currywurst'
+                    }
+                ]
+            }
+        }
+    )
+
+    t.is(actual, expected)
+})
+
+test('formatText test throws', t => {
+    const error = t.throws(() => {
+        formatText(
+            'This will give ${error.}', // eslint-disable-line no-template-curly-in-string
+            { error: [{}] }
+        )
+    }, SyntaxError)
+
+    t.is(error.message, '[formatText] failed to parse named argument key: error.')
+})