diff --git a/internal/driver/cli.go b/internal/driver/cli.go
index 4292b64b0..53231786f 100644
--- a/internal/driver/cli.go
+++ b/internal/driver/cli.go
@@ -15,6 +15,7 @@
 package driver
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -87,7 +88,7 @@ func parseFlags(o *plugin.Options) (*source, []string, error) {
 			usageMsgVars)
 	})
 	if len(args) == 0 {
-		return nil, nil, fmt.Errorf("no profile source specified")
+		return nil, nil, errors.New("no profile source specified")
 	}
 
 	var execName string
@@ -114,7 +115,7 @@ func parseFlags(o *plugin.Options) (*source, []string, error) {
 		return nil, nil, err
 	}
 	if cmd != nil && *flagHTTP != "" {
-		return nil, nil, fmt.Errorf("-http is not compatible with an output format on the command line")
+		return nil, nil, errors.New("-http is not compatible with an output format on the command line")
 	}
 
 	si := pprofVariables["sample_index"].value
@@ -148,7 +149,7 @@ func parseFlags(o *plugin.Options) (*source, []string, error) {
 
 	normalize := pprofVariables["normalize"].boolValue()
 	if normalize && len(source.Base) == 0 {
-		return nil, nil, fmt.Errorf("Must have base profile to normalize by")
+		return nil, nil, errors.New("Must have base profile to normalize by")
 	}
 	source.Normalize = normalize
 
@@ -162,17 +163,15 @@ func parseFlags(o *plugin.Options) (*source, []string, error) {
 // the source. This function will return an error if both base and diff base
 // profiles are specified.
 func (source *source) addBaseProfiles(flagBase, flagDiffBase []*string) error {
-	base := dropEmpty(flagBase)
-	diffBase := dropEmpty(flagDiffBase)
+	base, diffBase := dropEmpty(flagBase), dropEmpty(flagDiffBase)
 
 	if len(base) > 0 && len(diffBase) > 0 {
-		return fmt.Errorf("-base and -diff_base flags cannot both be specified")
+		return errors.New("-base and -diff_base flags cannot both be specified")
 	}
 
 	source.Base = base
 	if len(diffBase) > 0 {
-		source.Base = diffBase
-		source.DiffBase = true
+		source.Base, source.DiffBase = diffBase, true
 	}
 	return nil
 }
@@ -271,7 +270,7 @@ func outputFormat(bcmd map[string]*bool, acmd map[string]*string) (cmd []string,
 	for n, b := range bcmd {
 		if *b {
 			if cmd != nil {
-				return nil, fmt.Errorf("must set at most one output format")
+				return nil, errors.New("must set at most one output format")
 			}
 			cmd = []string{n}
 		}
@@ -279,7 +278,7 @@ func outputFormat(bcmd map[string]*bool, acmd map[string]*string) (cmd []string,
 	for n, s := range acmd {
 		if *s != "" {
 			if cmd != nil {
-				return nil, fmt.Errorf("must set at most one output format")
+				return nil, errors.New("must set at most one output format")
 			}
 			cmd = []string{n, *s}
 		}
diff --git a/internal/driver/fetch_test.go b/internal/driver/fetch_test.go
index b0fc51b06..e9e68e2a5 100644
--- a/internal/driver/fetch_test.go
+++ b/internal/driver/fetch_test.go
@@ -231,25 +231,25 @@ func TestFetchWithBase(t *testing.T) {
 			"not normalized base is same as source",
 			[]string{path + "cppbench.contention"},
 			[]string{path + "cppbench.contention"},
-			[]string{},
+			nil,
 			false,
-			[]WantSample{},
+			nil,
 			"",
 		},
 		{
 			"not normalized base is same as source",
 			[]string{path + "cppbench.contention"},
 			[]string{path + "cppbench.contention"},
-			[]string{},
+			nil,
 			false,
-			[]WantSample{},
+			nil,
 			"",
 		},
 		{
 			"not normalized single source, multiple base (all profiles same)",
 			[]string{path + "cppbench.contention"},
 			[]string{path + "cppbench.contention", path + "cppbench.contention"},
-			[]string{},
+			nil,
 			false,
 			[]WantSample{
 				{
@@ -283,7 +283,7 @@ func TestFetchWithBase(t *testing.T) {
 			"not normalized, different base and source",
 			[]string{path + "cppbench.contention"},
 			[]string{path + "cppbench.small.contention"},
-			[]string{},
+			nil,
 			false,
 			[]WantSample{
 				{
@@ -317,7 +317,7 @@ func TestFetchWithBase(t *testing.T) {
 			"normalized base is same as source",
 			[]string{path + "cppbench.contention"},
 			[]string{path + "cppbench.contention"},
-			[]string{},
+			nil,
 			true,
 			[]WantSample{},
 			"",
@@ -326,7 +326,7 @@ func TestFetchWithBase(t *testing.T) {
 			"normalized single source, multiple base (all profiles same)",
 			[]string{path + "cppbench.contention"},
 			[]string{path + "cppbench.contention", path + "cppbench.contention"},
-			[]string{},
+			nil,
 			true,
 			[]WantSample{},
 			"",
@@ -335,7 +335,7 @@ func TestFetchWithBase(t *testing.T) {
 			"normalized different base and source",
 			[]string{path + "cppbench.contention"},
 			[]string{path + "cppbench.small.contention"},
-			[]string{},
+			nil,
 			true,
 			[]WantSample{
 				{
@@ -368,7 +368,7 @@ func TestFetchWithBase(t *testing.T) {
 		{
 			"not normalized diff base is same as source",
 			[]string{path + "cppbench.contention"},
-			[]string{},
+			nil,
 			[]string{path + "cppbench.contention"},
 			false,
 			[]WantSample{
@@ -466,12 +466,12 @@ func TestFetchWithBase(t *testing.T) {
 
 		if tc.wantErrorMsg != "" {
 			if err == nil {
-				t.Errorf("%s: want error %q, got nil", tc.desc, tc.wantErrorMsg)
+				t.Errorf("%s: got nil, want error %q", tc.desc, tc.wantErrorMsg)
 				continue
 			}
 			gotErrMsg := err.Error()
 			if gotErrMsg != tc.wantErrorMsg {
-				t.Errorf("%s: want error %q, got error %q", tc.desc, tc.wantErrorMsg, gotErrMsg)
+				t.Errorf("%s: got error %q, want error %q", tc.desc, gotErrMsg, tc.wantErrorMsg)
 			}
 			continue
 		}
@@ -489,18 +489,16 @@ func TestFetchWithBase(t *testing.T) {
 		}
 
 		if want, got := len(tc.wantSamples), len(p.Sample); want != got {
-			t.Errorf("%s: want %d samples got %d", tc.desc, want, got)
+			t.Errorf("%s: got %d samples want %d", tc.desc, got, want)
 			continue
 		}
 
-		if len(p.Sample) > 0 {
-			for i, sample := range p.Sample {
-				if !reflect.DeepEqual(tc.wantSamples[i].values, sample.Value) {
-					t.Errorf("%s: for sample %d want values %v, got %v", tc.desc, i, tc.wantSamples[i], sample.Value)
-				}
-				if !reflect.DeepEqual(tc.wantSamples[i].labels, sample.Label) {
-					t.Errorf("%s: for sample %d want labels %v, got %v", tc.desc, i, tc.wantSamples[i].labels, sample.Label)
-				}
+		for i, sample := range p.Sample {
+			if !reflect.DeepEqual(tc.wantSamples[i].values, sample.Value) {
+				t.Errorf("%s: for sample %d got values %v, want %v", tc.desc, i, sample.Value, tc.wantSamples[i])
+			}
+			if !reflect.DeepEqual(tc.wantSamples[i].labels, sample.Label) {
+				t.Errorf("%s: for sample %d got labels %v, want %v", tc.desc, i, sample.Label, tc.wantSamples[i].labels)
 			}
 		}
 	}
diff --git a/internal/report/report_test.go b/internal/report/report_test.go
index 57e0bd266..9a6412004 100644
--- a/internal/report/report_test.go
+++ b/internal/report/report_test.go
@@ -401,7 +401,7 @@ func TestComputeTotal(t *testing.T) {
 		t.Run(tc.desc, func(t *testing.T) {
 			gotTotal := computeTotal(tc.prof, tc.value, tc.meanDiv)
 			if gotTotal != tc.wantTotal {
-				t.Errorf("want total %d, got %v", tc.wantTotal, gotTotal)
+				t.Errorf("got total %d, want %v", gotTotal, tc.wantTotal)
 			}
 		})
 	}