diff --git a/src/bytes/buffer_test.go b/src/bytes/buffer_test.go
index 81476fbae15d45..845e5e2209e53e 100644
--- a/src/bytes/buffer_test.go
+++ b/src/bytes/buffer_test.go
@@ -268,7 +268,7 @@ type panicReader struct{ panic bool }
 
 func (r panicReader) Read(p []byte) (int, error) {
 	if r.panic {
-		panic(nil)
+		panic("oops")
 	}
 	return 0, io.EOF
 }
diff --git a/src/crypto/internal/bigmod/nat_test.go b/src/crypto/internal/bigmod/nat_test.go
index 6431d259547cc3..4593a2e4932795 100644
--- a/src/crypto/internal/bigmod/nat_test.go
+++ b/src/crypto/internal/bigmod/nat_test.go
@@ -181,7 +181,7 @@ func TestSetBytes(t *testing.T) {
 			}
 			continue
 		}
-		if err == nil && tt.fail {
+		if tt.fail {
 			t.Errorf("%d: unexpected success", i)
 			continue
 		}
diff --git a/src/encoding/xml/xml_test.go b/src/encoding/xml/xml_test.go
index 8205ac31484d84..f5c7259cfb45c1 100644
--- a/src/encoding/xml/xml_test.go
+++ b/src/encoding/xml/xml_test.go
@@ -1359,8 +1359,9 @@ func TestParseErrors(t *testing.T) {
 			}
 			continue
 		}
-		if err == nil || err == io.EOF {
-			t.Errorf("parse %s: have no error, expected a non-nil error", test.src)
+		// Inv: err != nil
+		if err == io.EOF {
+			t.Errorf("parse %s: unexpected EOF", test.src)
 			continue
 		}
 		if !strings.Contains(err.Error(), test.err) {
diff --git a/src/net/timeout_test.go b/src/net/timeout_test.go
index 6b3554ed7987e7..89605d92fc7679 100644
--- a/src/net/timeout_test.go
+++ b/src/net/timeout_test.go
@@ -812,10 +812,11 @@ func TestWriteTimeoutFluctuation(t *testing.T) {
 		t.Logf("SetWriteDeadline(+%v)", d)
 		t0 := time.Now()
 		deadline := t0.Add(d)
-		if err = c.SetWriteDeadline(deadline); err != nil {
+		if err := c.SetWriteDeadline(deadline); err != nil {
 			t.Fatalf("SetWriteDeadline(%v): %v", deadline, err)
 		}
 		var n int64
+		var err error
 		for {
 			var dn int
 			dn, err = c.Write([]byte("TIMEOUT TRANSMITTER"))
@@ -825,8 +826,8 @@ func TestWriteTimeoutFluctuation(t *testing.T) {
 			}
 		}
 		t1 := time.Now()
-
-		if err == nil || !err.(Error).Timeout() {
+		// Inv: err != nil
+		if !err.(Error).Timeout() {
 			t.Fatalf("Write did not return (any, timeout): (%d, %v)", n, err)
 		}
 		if perr := parseWriteError(err); perr != nil {
diff --git a/src/os/timeout_test.go b/src/os/timeout_test.go
index 3cf06d56477364..a65d703ebfa969 100644
--- a/src/os/timeout_test.go
+++ b/src/os/timeout_test.go
@@ -355,10 +355,11 @@ func TestWriteTimeoutFluctuation(t *testing.T) {
 		t.Logf("SetWriteDeadline(+%v)", d)
 		t0 := time.Now()
 		deadline := t0.Add(d)
-		if err = w.SetWriteDeadline(deadline); err != nil {
+		if err := w.SetWriteDeadline(deadline); err != nil {
 			t.Fatalf("SetWriteDeadline(%v): %v", deadline, err)
 		}
 		var n int64
+		var err error
 		for {
 			var dn int
 			dn, err = w.Write([]byte("TIMEOUT TRANSMITTER"))
@@ -368,8 +369,8 @@ func TestWriteTimeoutFluctuation(t *testing.T) {
 			}
 		}
 		t1 := time.Now()
-
-		if err == nil || !isDeadlineExceeded(err) {
+		// Inv: err != nil
+		if !isDeadlineExceeded(err) {
 			t.Fatalf("Write did not return (any, timeout): (%d, %v)", n, err)
 		}
 
diff --git a/src/testing/example.go b/src/testing/example.go
index f618b06de114b0..42ee555cb28f7d 100644
--- a/src/testing/example.go
+++ b/src/testing/example.go
@@ -93,8 +93,7 @@ func (eg *InternalExample) processRunResult(stdout string, timeSpent time.Durati
 	if recovered != nil {
 		// Propagate the previously recovered result, by panicking.
 		panic(recovered)
-	}
-	if !finished && recovered == nil {
+	} else if !finished {
 		panic(errNilPanicOrGoexit)
 	}