2 files changed, 54 insertions, 1 deletions
diff --git a/__tests__/dice.test.js b/__tests__/dice.test.js
index 3073fee..6ff86e7 100644
--- a/__tests__/dice.test.js
+++ b/__tests__/dice.test.js
@@ -8,7 +8,8 @@ const {
   explode,
   keepHigh,
   keepLow,
-  bonusAdd
+  bonusAdd,
+  bonusSubtract
 } = require('../src/dice.js')
 
 const defaultNumberRolls = 500
@@ -493,3 +494,43 @@ describe('bonusAdd', () => {
     })
   })
 })
+
+describe('bonusSubtract', () => {
+  describe('1d20-3', () => {
+    const die = bonusSubtract(d(constant(1), constant(20)), constant(3))
+    testDie(die, {
+      diceCount: 1,
+      average: {
+        average: 7.5
+      },
+      variance: {
+        variance: 33.25
+      },
+      bounds: {
+        low: -2,
+        high: 17,
+        expectLow: true,
+        expectHigh: true
+      }
+    })
+  })
+
+  describe('3d4-1', () => {
+    const die = bonusSubtract(d(constant(3), constant(4)), constant(1))
+    testDie(die, {
+      diceCount: 3,
+      average: {
+        average: 4.5
+      },
+      variance: {
+        variance: 3.75
+      },
+      bounds: {
+        low: 0,
+        high: 9,
+        expectLow: true,
+        expectHigh: true
+      }
+    })
+  })
+})
diff --git a/__tests__/parser.test.js b/__tests__/parser.test.js
index 873972b..54e1da7 100644
--- a/__tests__/parser.test.js
+++ b/__tests__/parser.test.js
@@ -163,6 +163,18 @@ describe('parse', () => {
     })
   })
 
+  it('parses negative bonuses', () => {
+    expect(parse('3d4-1')).toEqual({
+      type: 'bonusSubtract',
+      left: {
+        type: 'd',
+        left: { type: 'constant', value: 3 },
+        right: { type: 'constant', value: 4 }
+      },
+      right: { type: 'constant', value: 1 }
+    })
+  })
+
   describe('parsing parentheses', () => {
     test('(1d6)d6', () => {
       expect(parse('(1d6)d6')).toEqual({