add tests for amount filters

frontend/src/filters/amount.js

@@ -12,6 +12,7 @@ const amount = (value) => {
 
 const GDD = (value) => {
   value = amount(value)
+  if (value === '') return ''
   if (!value.match(/^− /)) value = '+ ' + value
   return value + ' GDD'
 }

frontend/src/filters/amount.test.js

@@ -0,0 +1,35 @@
+import { loadFilters } from './amount'
+
+const i18nMock = {
+  n: jest.fn((n) => n),
+}
+
+const { amount, GDD } = loadFilters(i18nMock)
+
+describe('amount', () => {
+  it('returns empty string when called with null', () => {
+    expect(amount(null)).toBe('')
+  })
+
+  it('returns 0 when called with 0', () => {
+    expect(amount(0)).toBe('0')
+  })
+
+  it('returns a leading proper minus sign when called with negative value', () => {
+    expect(amount(-1)).toBe('− 1')
+  })
+})
+
+describe('GDD', () => {
+  it('returns empty string when called with null', () => {
+    expect(GDD(null)).toBe('')
+  })
+
+  it('returns "+ 0 GDD" when called with 0', () => {
+    expect(GDD(0)).toBe('+ 0 GDD')
+  })
+
+  it('returns a leading proper minus sign when called with negative value', () => {
+    expect(GDD(-1)).toBe('− 1 GDD')
+  })
+})