Tidy assert package.

+ Rename some functions to make sense:
  + Error now asserts that an error *did* occur.
  + NoError was added to assert that an error did *not* occur.
  + Error2 has been renamed ErrorEq.
+ More documentation added to clarify things.
+ Certain functions take optional strings to describe what went wrong.

assert/assert.go

@@ -1,41 +1,81 @@
 // Package assert provides C-like assertions for Go. For more
 // information, see assert(3) (e.g. `man 3 assert`).
+//
+// The T variants operating on *testing.T values; instead of killing
+// the program, they call the Fatal method.
 package assert
 
 import (
 	"fmt"
 	"os"
 	"runtime"
+	"strings"
 	"testing"
 )
 
 // NoDebug, if set to true, will cause all asserts to be ignored.
 var NoDebug bool
 
-func die(what string) {
+func die(what string, a ...string) {
 	_, file, line, ok := runtime.Caller(2)
 	if !ok {
 		panic(what)
 	} else {
-		fmt.Fprintf(os.Stderr, "%s\n", what)
+		fmt.Fprintf(os.Stderr, "%s", what)
+		if len(a) > 0 {
+			s := strings.Join(a, ", ")
+			fmt.Fprintln(os.Stderr, ":"+s)
+		} else {
+			fmt.Fprintf(os.Stderr, "\n")
+		}
 		fmt.Fprintf(os.Stderr, "\t%s line %d\n", file, line)
 		os.Exit(1)
 	}
 }
 
 // Bool asserts that cond is false.
-func Bool(cond bool) {
+//
+// For example, this would replace
+//    if x < 0 {
+//            log.Fatal("x is subzero")
+//    }
+//
+// The same assertion would be
+//    assert.Bool(x, "x is subzero")
+func Bool(cond bool, s ...string) {
 	if NoDebug {
 		return
 	}
 
 	if !cond {
-		die("assert.Bool failed")
+		die("assert.Bool failed", s...)
 	}
 }
 
-// Error asserts that err is nil.
-func Error(err error) {
+// Error asserts that err is not nil, e.g. that an error has occurred.
+//
+// For example,
+//     if err == nil {
+//             log.Fatal("call to <something> should have failed")
+//     }
+//     // becomes
+//     assert.Error(err, "call to <something> should have failed")
+func Error(err error, s ...string) {
+	if NoDebug {
+		return
+	} else if nil != err {
+		return
+	}
+
+	if len(s) == 0 {
+		die("error expected, but no error returned")
+	} else {
+		die(strings.Join(s, ", "))
+	}
+}
+
+// NoError asserts that err is nil, e.g. that no error has occurred.
+func NoError(err error, s ...string) {
 	if NoDebug {
 		return
 	}
@@ -45,14 +85,14 @@ func Error(err error) {
 	}
 }
 
-// Error2 asserts that the actual error is the expected error.
-func Error2(expected, actual error) {
+// ErrorEq asserts that the actual error is the expected error.
+func ErrorEq(expected, actual error) {
 	if NoDebug || (expected == actual) {
 		return
 	}
 
 	if expected == nil {
-		die(fmt.Sprintf("assert.Error2: %s", actual.Error()))
+		die(fmt.Sprintf("assert.ErrorEq: %s", actual.Error()))
 	}
 
 	var should string
@@ -62,28 +102,46 @@ func Error2(expected, actual error) {
 		should = fmt.Sprintf("have '%s'", actual)
 	}
 
-	die(fmt.Sprintf("assert.Error2: expected '%s', but %s", expected, should))
+	die(fmt.Sprintf("assert.ErrorEq: expected '%s', but %s", expected, should))
 }
 
 // BoolT checks a boolean condition, calling Fatal on t if it is
 // false.
-func BoolT(t *testing.T, cond bool) {
+func BoolT(t *testing.T, cond bool, s ...string) {
 	if !cond {
-		t.Fatal("assert.Bool failed")
+		what := strings.Join(s, ", ")
+		if len(what) > 0 {
+			what = ": " + what
+		}
+		t.Fatalf("assert.Bool failed%s", what)
 	}
 }
 
-// ErrorT checks whether the error is nil, calling Fatal on t if it
-// isn't.
-func ErrorT(t *testing.T, err error) {
+// ErrorT asserts that err is not nil, e.g. asserting that an error
+// has occurred. See also NoErrorT.
+func ErrorT(t *testing.T, err error, s ...string) {
+	if nil != err {
+		return
+	}
+
+	if len(s) == 0 {
+		t.Fatal("error expected, but no error returned")
+	} else {
+		t.Fatal(strings.Join(s, ", "))
+	}
+}
+
+// NoErrorT asserts that err is nil, e.g. asserting that no error has
+// occurred. See also ErrorT.
+func NoErrorT(t *testing.T, err error) {
 	if nil != err {
 		t.Fatalf("%s", err)
 	}
 }
 
-// Error2T compares a pair of errors, calling Fatal on it if they
+// ErrorEqT compares a pair of errors, calling Fatal on it if they
 // don't match.
-func Error2T(t *testing.T, expected, actual error) {
+func ErrorEqT(t *testing.T, expected, actual error) {
 	if NoDebug || (expected == actual) {
 		return
 	}