catalog: Improve position report's Course

* Add func NewCourse() ("constructor")
* Code cleanup
* Tests

catalog/position_report.go

@@ -7,6 +7,7 @@ package catalog
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"math"
 	"time"
@@ -27,11 +28,23 @@ type Course struct {
 	Magnetic bool
 }
 
+func NewCourse(degrees int, magnetic bool) (*Course, error) {
+	if degrees < 0 || degrees > 360 {
+		return nil, errors.New("degrees out of bounds [0,360]")
+	}
+	if degrees == 360 {
+		degrees = 0
+	}
+	c := Course{Magnetic: magnetic}
+	copy(c.Digits[:], []byte(fmt.Sprintf("%3d", degrees)))
+	return &c, nil
+}
+
 func (c Course) String() string {
 	if c.Magnetic {
-		return fmt.Sprintf("%sM", string(c.Digits[:3]))
+		return fmt.Sprintf("%sM", string(c.Digits[:]))
 	} else {
-		return fmt.Sprintf("%sT", string(c.Digits[:3]))
+		return fmt.Sprintf("%sT", string(c.Digits[:]))
 	}
 }
 

catalog/position_report_test.go

@@ -41,6 +41,40 @@ func TestDecToDM(t *testing.T) {
 	}
 }
 
+func omitErr(v *Course, _ error) *Course { return v }
+
+func TestCourseStringer2(t *testing.T) {
+	// omitErr := func(c *Course, err error) *Course { return c }
+	tests := map[string]*Course{
+		"123T": omitErr(NewCourse(123, false)),
+		"123M": omitErr(NewCourse(123, true)),
+	}
+	for expect, in := range tests {
+		t.Run(expect, func(t *testing.T) {
+			if in == nil && expect != "" {
+				t.Fatal("got unexpected nil")
+			}
+			if got := in.String(); got != expect {
+				t.Errorf("Got %q, expected %q", got, expect)
+			}
+		})
+	}
+}
+
+func TestCourseStringer(t *testing.T) {
+	tests := map[string]Course{
+		"123T": {Digits: [3]byte{'1', '2', '3'}, Magnetic: false},
+		"123M": {Digits: [3]byte{'1', '2', '3'}, Magnetic: true},
+	}
+	for expect, in := range tests {
+		t.Run(expect, func(t *testing.T) {
+			if got := in.String(); got != expect {
+				t.Errorf("Got %q, expected %q", got, expect)
+			}
+		})
+	}
+}
+
 func ExamplePosReport_Message() {
 	lat := 60.18
 	lon := 5.3972