fix: Parse YDS slash grades correctly

YDS slash grades were being assigned the score of the first grade. This
was due to `.includes()` not matching the slash.

Change this to correctly identify slash grades.  Refactor a little to
help clarity.
Add test that score range of a slash grade is strict subset of that of
the two grades, and overlaps with both of them.

Add failing tests slash grades composed of non-consecutive grades and
slashes across number boundaries.

Fixes #142

src/__tests__/scales/yds.ts

@@ -70,6 +70,15 @@ describe('YosemiteDecimal', () => {
     test('grade with slash', () => {
       expect(YosemiteDecimal.isType('5.10a/b')).toBeTruthy()
     })
+    test.failing('grade with slash', () => {
+      expect(YosemiteDecimal.isType('5.10d/5.11a')).toBeTruthy()
+    })
+
+    test.failing('grade with non-consecutive slash grades', () => {
+      expect(YosemiteDecimal.isType('5.10d/c')).toBeFalsy()
+      expect(YosemiteDecimal.isType('5.10a/c')).toBeFalsy()
+      expect(YosemiteDecimal.isType('5.10c/5.11a')).toBeFalsy()
+    })
 
     test('incorrect type', () => {
       expect(YosemiteDecimal.isType('11+')).toBeFalsy()
@@ -112,4 +121,17 @@ describe('YosemiteDecimal', () => {
       expect(YosemiteDecimal.getGradeBand('5.15a')).toEqual(GradeBands.EXPERT)
     })
   })
+
+  describe('Slash scores', () => {
+    test('scores of slash grades should be subset of neighboring scores', () => {
+      const slashScore = YosemiteDecimal.getScore('5.10a/b')
+      const lowScore = YosemiteDecimal.getScore('5.10a')
+      const highScore = YosemiteDecimal.getScore('5.10b')
+
+      expect(slashScore[0]).toBeGreaterThan(lowScore[0])
+      expect(slashScore[1]).toBeGreaterThan(lowScore[1])
+      expect(slashScore[0]).toBeLessThan(highScore[0])
+      expect(slashScore[1]).toBeLessThan(highScore[1])
+    })
+  })
 })

src/scales/yds.ts

@@ -66,32 +66,35 @@ const getScore = (grade: string): number | Tuple => {
   }
   const [wholeMatch, basicGrade, number, letter, plusOrMinusOrSlash] = parse
   let normalizedGrade = basicGrade
-  const plusSlash = ['+', '/'].includes(plusOrMinusOrSlash)
+
+  const slash = plusOrMinusOrSlash?.startsWith('/')
   const minus = plusOrMinusOrSlash === '-'
+  const plus = plusOrMinusOrSlash === '+'
+
   let normalizedLetter = letter
   const isLargeNonLetter = parseInt(number, 10) > 9 && normalizedLetter === ''
   if (isLargeNonLetter) {
     // 11-, 13+, 12
-    normalizedLetter = minus ? 'a' : plusSlash ? 'c' : 'b'
+    normalizedLetter = minus ? 'a' : (plus || slash) ? 'c' : 'b'
   }
   normalizedGrade = basicGrade + normalizedLetter
   const basicScore = findScoreRange((r: Route) => {
     return r.yds === normalizedGrade
   }, routes)
 
   if (wholeMatch !== normalizedGrade) {
-    let otherGrade
-    // 5.11+, 5.10a/b
-    if (plusSlash || isLargeNonLetter) {
-      otherGrade = (typeof basicScore === 'number' ? basicScore : basicScore[1]) + 1
+    let otherScore
+    if (plus || slash || isLargeNonLetter) {
+      // 5.11+, 5.10a/b
+      otherScore = (typeof basicScore === 'number' ? basicScore : basicScore[1]) + 1
     } else if (minus) {
       // 5.11-
-      otherGrade = (typeof basicScore === 'number' ? basicScore : basicScore[0]) - 1
+      otherScore = (typeof basicScore === 'number' ? basicScore : basicScore[0]) - 1
     }
 
-    if (otherGrade !== undefined) {
+    if (otherScore !== undefined) {
       const nextGrade = findScoreRange((r: Route) => {
-        return r.yds.toLowerCase() === routes[Math.max(otherGrade, 0)].yds.toLowerCase()
+        return r.yds.toLowerCase() === routes[Math.max(otherScore, 0)].yds.toLowerCase()
       }, routes)
       return [getAvgScore(basicScore), getAvgScore(nextGrade)].sort((a, b) => a - b) as Tuple
     }