Add MustReadFile utility (#162)

* Add MustReadFile utility

* Comment

testingx/testdata/valid-file.txt

@@ -0,0 +1 @@
+foo

testingx/testingx.go

@@ -2,6 +2,7 @@ package testingx
 
 import (
 	"fmt"
+	"os"
 )
 
 // FatalReporter defines the interface for reporting a fatal test.
@@ -16,12 +17,15 @@ type FatalReporter interface {
 // a format string.
 //
 // The main purpose of this function is to turn the common pattern of:
-//    err := Func()
-//    if err != nil {
-//        t.Fatalf("Helpful message (error: %v)", err)
-//    }
+//
+//	err := Func()
+//	if err != nil {
+//	    t.Fatalf("Helpful message (error: %v)", err)
+//	}
+//
 // into a simplified pattern of:
-//    Must(t, Func(), "Helpful message")
+//
+//	Must(t, Func(), "Helpful message")
 //
 // This has the benefit of using fewer lines and verifying unit tests are
 // "correct by inspection".
@@ -35,3 +39,11 @@ func Must(t FatalReporter, err error, prefix string, args ...interface{}) {
 		t.Fatal(prefix + suffix)
 	}
 }
+
+// MustReadFile will read the file under the input `path` and return the array
+// of bytes. If it fails, it will call t.Fatal.
+func MustReadFile(t FatalReporter, path string) []byte {
+	file, err := os.ReadFile(path)
+	Must(t, err, "")
+	return file
+}

testingx/testingx_test.go

@@ -1,6 +1,7 @@
 package testingx
 
 import (
+	"bytes"
 	"errors"
 	"testing"
 )
@@ -28,3 +29,24 @@ func TestMust(t *testing.T) {
 		}
 	})
 }
+
+func TestMustReadFile_Success(t *testing.T) {
+	f := &fakeReporter{}
+	got := MustReadFile(f, "./testdata/valid-file.txt")
+	if f.called != 0 {
+		t.Fatal("MustReadFile() t.Fatal called for valid file")
+	}
+
+	want := []byte("foo")
+	if !bytes.Equal(got, want) {
+		t.Fatalf("MustReadFile() got = %s, want = %s", string(got), string(want))
+	}
+}
+
+func TestMustReadFile_Error(t *testing.T) {
+	f := &fakeReporter{}
+	MustReadFile(f, "./testdata/invalid-file.txt")
+	if f.called != 1 {
+		t.Fatal("MustReadFile() t.Fatal NOT called for invalid file")
+	}
+}