[chore]: enable error-nil rule from testifylint (#5843)

Testifylint is a linter that provides best practices with the use of
testify.

This PR enables
[error-nil](https://github.com/Antonboom/testifylint?tab=readme-ov-file#error-nil)
rule from [testifylint](https://github.com/Antonboom/testifylint)

Signed-off-by: Matthieu MOREL <matthieu.morel35@gmail.com>
Co-authored-by: Robert Pająk <pellared@hotmail.com>

.golangci.yml

@@ -306,7 +306,6 @@ linters-settings:
   testifylint:
     enable-all: true
     disable:
-      - error-nil
       - expected-actual
       - float-compare
       - go-require

bridge/opencensus/metric_test.go

@@ -131,7 +131,7 @@ func TestMetricProducer(t *testing.T) {
 			if tc.expectErr {
 				require.Error(t, err)
 			} else {
-				require.Nil(t, err)
+				require.NoError(t, err)
 			}
 			require.Equal(t, len(output), len(tc.expected))
 			for i := range output {

exporters/otlp/otlpmetric/otlpmetricgrpc/internal/partialsuccess_test.go

@@ -15,7 +15,6 @@ import (
 
 func requireErrorString(t *testing.T, expect string, err error) {
 	t.Helper()
-	require.NotNil(t, err)
 	require.Error(t, err)
 	require.ErrorIs(t, err, PartialSuccess{})
 

exporters/otlp/otlpmetric/otlpmetricgrpc/internal/transform/error_test.go

@@ -35,7 +35,7 @@ func TestMultiErr(t *testing.T) {
 	me := &multiErr{datatype: name}
 
 	t.Run("ErrOrNil", func(t *testing.T) {
-		require.Nil(t, me.errOrNil())
+		require.NoError(t, me.errOrNil())
 		me.errs = []error{e0}
 		assert.Error(t, me.errOrNil())
 	})

exporters/otlp/otlpmetric/otlpmetrichttp/internal/partialsuccess_test.go

@@ -15,7 +15,6 @@ import (
 
 func requireErrorString(t *testing.T, expect string, err error) {
 	t.Helper()
-	require.NotNil(t, err)
 	require.Error(t, err)
 	require.ErrorIs(t, err, PartialSuccess{})
 

exporters/otlp/otlpmetric/otlpmetrichttp/internal/transform/error_test.go

@@ -35,7 +35,7 @@ func TestMultiErr(t *testing.T) {
 	me := &multiErr{datatype: name}
 
 	t.Run("ErrOrNil", func(t *testing.T) {
-		require.Nil(t, me.errOrNil())
+		require.NoError(t, me.errOrNil())
 		me.errs = []error{e0}
 		assert.Error(t, me.errOrNil())
 	})

exporters/otlp/otlptrace/otlptracegrpc/internal/partialsuccess_test.go

@@ -15,7 +15,6 @@ import (
 
 func requireErrorString(t *testing.T, expect string, err error) {
 	t.Helper()
-	require.NotNil(t, err)
 	require.Error(t, err)
 	require.ErrorIs(t, err, PartialSuccess{})
 

exporters/otlp/otlptrace/otlptracehttp/internal/partialsuccess_test.go

@@ -15,7 +15,6 @@ import (
 
 func requireErrorString(t *testing.T, expect string, err error) {
 	t.Helper()
-	require.NotNil(t, err)
 	require.Error(t, err)
 	require.ErrorIs(t, err, PartialSuccess{})
 

exporters/stdout/stdouttrace/trace_test.go

@@ -88,7 +88,7 @@ func TestExporterExportSpan(t *testing.T) {
 		// write to buffer for testing
 		var b bytes.Buffer
 		ex, err := stdouttrace.New(append(tt.opts, stdouttrace.WithWriter(&b))...)
-		require.Nil(t, err)
+		require.NoError(t, err)
 
 		err = ex.ExportSpans(tt.ctx, tracetest.SpanStubs{ss, ss}.Snapshots())
 		assert.Equal(t, tt.wantErr, err)

internal/shared/otlp/otlpmetric/transform/error_test.go.tmpl

@@ -35,7 +35,7 @@ func TestMultiErr(t *testing.T) {
 	me := &multiErr{datatype: name}
 
 	t.Run("ErrOrNil", func(t *testing.T) {
-		require.Nil(t, me.errOrNil())
+		require.NoError(t, me.errOrNil())
 		me.errs = []error{e0}
 		assert.Error(t, me.errOrNil())
 	})

internal/shared/otlp/partialsuccess_test.go.tmpl

@@ -15,7 +15,6 @@ import (
 
 func requireErrorString(t *testing.T, expect string, err error) {
 	t.Helper()
-	require.NotNil(t, err)
 	require.Error(t, err)
 	require.ErrorIs(t, err, PartialSuccess{})
 

sdk/metric/config_test.go

@@ -55,8 +55,8 @@ func TestConfigReaderSignalsEmpty(t *testing.T) {
 	require.NotNil(t, s)
 
 	ctx := context.Background()
-	assert.Nil(t, f(ctx))
-	assert.Nil(t, s(ctx))
+	assert.NoError(t, f(ctx))
+	assert.NoError(t, s(ctx))
 	assert.ErrorIs(t, s(ctx), ErrReaderShutdown)
 }
 

sdk/trace/provider_test.go

@@ -370,7 +370,7 @@ func testStoredError(t *testing.T, target interface{}) {
 		err := handler.errs[0]
 
 		require.Implements(t, (*error)(nil), target)
-		require.NotNil(t, target.(error))
+		require.Error(t, target.(error))
 
 		defer handler.Reset()
 		if errors.Is(err, target.(error)) {