Improve testutil error messages

This also satisfy newer staticcheck versions.

Signed-off-by: beorn7 <beorn@soundcloud.com>

prometheus/testutil/testutil.go

@@ -165,11 +165,9 @@ func compare(got, want []*dto.MetricFamily) error {
 metric output does not match expectation; want:
 
 %s
-
 got:
 
-%s
-`, wantBuf.String(), gotBuf.String())
+%s`, wantBuf.String(), gotBuf.String())
 
 	}
 	return nil

prometheus/testutil/testutil_test.go

@@ -171,7 +171,6 @@ func TestCollectAndCompareHistogram(t *testing.T) {
 		c           prometheus.Collector
 		metadata    string
 		expect      string
-		labels      []string
 		observation float64
 	}{
 		{
@@ -291,13 +290,11 @@ metric output does not match expectation; want:
 # TYPE some_other_metric counter
 some_other_metric{label1="value1"} 1.0
 
-
 got:
 
 # HELP some_total A value that represents a counter.
 # TYPE some_total counter
 some_total{label1="value1"} 1.0
-
 `
 
 	err := CollectAndCompare(c, strings.NewReader(metadata+expected))
@@ -306,6 +303,6 @@ some_total{label1="value1"} 1.0
 	}
 
 	if err.Error() != expectedError {
-		t.Errorf("Expected\n%#+v\nGot:\n%#+v\n", expectedError, err.Error())
+		t.Errorf("Expected\n%#+v\nGot:\n%#+v", expectedError, err.Error())
 	}
 }