lapack/testlapack: use worklen type in DgetriTest

... and make worklen type a Stringer.

lapack/testlapack/dgetri.go

@@ -57,22 +57,19 @@ func DgetriTest(t *testing.T, impl Dgetrier) {
 		// Compute LU decomposition.
 		impl.Dgetrf(n, n, a, lda, ipiv)
 		// Test with various workspace sizes.
-		for size := range []int{0, 1, 2} {
+		for _, wl := range []worklen{minimumWork, mediumWork, optimumWork} {
 			ainv := make([]float64, len(a))
 			copy(ainv, a)
 
 			var lwork int
-			switch size {
-			case 0:
-				// Minimum workspace size.
+			switch wl {
+			case minimumWork:
 				lwork = max(1, n)
-			case 1:
-				// Medium workspace size.
+			case mediumWork:
 				work := make([]float64, 1)
 				impl.Dgetri(n, ainv, lda, ipiv, work, -1)
 				lwork = max(int(work[0])-2*n, n)
-			case 2:
-				// Optimum workspace size.
+			case optimumWork:
 				work := make([]float64, 1)
 				impl.Dgetri(n, ainv, lda, ipiv, work, -1)
 				lwork = int(work[0])

lapack/testlapack/general.go

@@ -50,6 +50,18 @@ const (
 	optimumWork
 )
 
+func (wl worklen) String() string {
+	switch wl {
+	case minimumWork:
+		return "minimum"
+	case mediumWork:
+		return "medium"
+	case optimumWork:
+		return "optimum"
+	}
+	return ""
+}
+
 // nanSlice allocates a new slice of length n filled with NaN.
 func nanSlice(n int) []float64 {
 	s := make([]float64, n)