diff --git a/Makefile b/Makefile
index 3e163cde..db2bf4a0 100644
--- a/Makefile
+++ b/Makefile
@@ -21,6 +21,11 @@ clean: # Clean up artifacts of the development environment to allow for untainte
 	go clean -i -race $(PACKAGE)
 .PHONY: clean
 
+editor: # Open our default IDE with the project's configuration.
+	@# WORKAROUND VS.code does not call Delve with absolute paths to files which it needs to set breakpoints. Until either Delve or VS.code have a fix we need to disable "-trimpath" which converts absolute to relative paths of Go builds which is a requirement for reproducible builds.
+	GOFLAGS="$(GOFLAGS) -trimpath=false" $(ROOT_DIR)/scripts/editor.sh
+.PHONY: editor
+
 help: # Show this help message.
 	@grep -E '^[a-zA-Z-][a-zA-Z0-9.-]*?:.*?# (.+)' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?# "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'
 .PHONY: help
diff --git a/evaluate/metrics/assessment.go b/evaluate/metrics/assessment.go
index f951345c..4257f87e 100644
--- a/evaluate/metrics/assessment.go
+++ b/evaluate/metrics/assessment.go
@@ -24,26 +24,30 @@ var (
 	AssessmentKeyNoExcessResponse = RegisterAssessmentKey("no-excess-response")
 )
 
-// Assessments holds numerical assessment metrics.
+// Assessments holds a collection of numerical assessment metrics.
 type Assessments map[AssessmentKey]uint
 
-// Merge combines two assessments into a new assessment and returns it.
-func (a Assessments) Merge(o Assessments) Assessments {
-	if a == nil {
-		a = Assessments{}
-	}
-	if o == nil {
-		o = Assessments{}
-	}
+// NewAssessments create a new assessment collection.
+func NewAssessments() Assessments {
+	return map[AssessmentKey]uint{}
+}
 
-	assessments := map[AssessmentKey]uint{}
+// Add adds the given assessment collection to the current one.
+func (a Assessments) Add(x Assessments) {
+	for k, v := range x {
+		a[k] += v
+	}
+}
 
-	for _, k := range allAssessmentKeys {
-		assessments[k] = a[k]
+// Merge combines two assessment collections into a new assessment collection and returns the new assessment collection.
+func Merge(a Assessments, b Assessments) (c Assessments) {
+	c = NewAssessments()
+	if a != nil {
+		c.Add(a)
 	}
-	for _, k := range allAssessmentKeys {
-		assessments[k] = o[k]
+	if b != nil {
+		c.Add(b)
 	}
 
-	return Assessments(assessments)
+	return c
 }
diff --git a/evaluate/metrics/assessment_test.go b/evaluate/metrics/assessment_test.go
new file mode 100644
index 00000000..5677d09b
--- /dev/null
+++ b/evaluate/metrics/assessment_test.go
@@ -0,0 +1,116 @@
+package metrics
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestAssessmentsAdd(t *testing.T) {
+	type testCase struct {
+		Name string
+
+		Assessments Assessments
+		X           Assessments
+
+		ExpectedAssessments Assessments
+	}
+
+	validate := func(t *testing.T, tc *testCase) {
+		t.Run(tc.Name, func(t *testing.T) {
+			tc.Assessments.Add(tc.X)
+
+			assert.Equal(t, tc.Assessments, tc.ExpectedAssessments)
+		})
+	}
+
+	validate(t, &testCase{
+		Name: "Empty",
+
+		Assessments: NewAssessments(),
+		X:           NewAssessments(),
+
+		ExpectedAssessments: NewAssessments(),
+	})
+
+	validate(t, &testCase{
+		Name: "Non existing key",
+
+		Assessments: NewAssessments(),
+		X: map[AssessmentKey]uint{
+			AssessmentKeyNoExcessResponse: 1,
+		},
+
+		ExpectedAssessments: map[AssessmentKey]uint{
+			AssessmentKeyNoExcessResponse: 1,
+		},
+	})
+
+	validate(t, &testCase{
+		Name: "Existing key",
+
+		Assessments: map[AssessmentKey]uint{
+			AssessmentKeyNoExcessResponse: 1,
+		},
+		X: map[AssessmentKey]uint{
+			AssessmentKeyNoExcessResponse: 1,
+		},
+
+		ExpectedAssessments: map[AssessmentKey]uint{
+			AssessmentKeyNoExcessResponse: 2,
+		},
+	})
+}
+
+func TestMerge(t *testing.T) {
+	type testCase struct {
+		Name string
+
+		A Assessments
+		B Assessments
+
+		ExpectedC Assessments
+	}
+
+	validate := func(t *testing.T, tc *testCase) {
+		t.Run(tc.Name, func(t *testing.T) {
+			actualC := Merge(tc.A, tc.B)
+
+			assert.Equal(t, tc.ExpectedC, actualC)
+		})
+	}
+
+	validate(t, &testCase{
+		Name: "Empty",
+
+		ExpectedC: NewAssessments(),
+	})
+
+	validate(t, &testCase{
+		Name: "Non existing key",
+
+		A: NewAssessments(),
+		B: map[AssessmentKey]uint{
+			AssessmentKeyNoExcessResponse: 1,
+		},
+
+		ExpectedC: map[AssessmentKey]uint{
+			AssessmentKeyNoExcessResponse: 1,
+		},
+	})
+
+	validate(t, &testCase{
+		Name: "Existing key",
+
+		A: map[AssessmentKey]uint{
+			AssessmentKeyNoExcessResponse: 1,
+		},
+		B: map[AssessmentKey]uint{
+			AssessmentKeyNoExcessResponse: 1,
+		},
+
+		ExpectedC: map[AssessmentKey]uint{
+			AssessmentKeyNoExcessResponse: 2,
+		},
+	})
+}
diff --git a/evaluate/metrics/metrics.go b/evaluate/metrics/metrics.go
index 3967bc06..1ae422c8 100644
--- a/evaluate/metrics/metrics.go
+++ b/evaluate/metrics/metrics.go
@@ -38,7 +38,7 @@ func (m Metrics) Add(o Metrics) Metrics {
 
 		Coverage: append(m.Coverage, o.Coverage...),
 
-		Assessments: m.Assessments.Merge(o.Assessments),
+		Assessments: Merge(m.Assessments, o.Assessments),
 	}
 }
 
diff --git a/evaluate/repository.go b/evaluate/repository.go
index db5acc7b..ba564912 100644
--- a/evaluate/repository.go
+++ b/evaluate/repository.go
@@ -53,7 +53,7 @@ func EvaluateRepository(model model.Model, language language.Language, repositor
 
 			continue
 		}
-		metrics.Assessments = metrics.Assessments.Merge(assessments)
+		metrics.Assessments.Add(assessments)
 
 		coverage, err := language.Execute(temporaryRepositoryPath)
 		if err != nil {
diff --git a/scripts/editor.sh b/scripts/editor.sh
new file mode 100755
index 00000000..4de80b88
--- /dev/null
+++ b/scripts/editor.sh
@@ -0,0 +1,7 @@
+#!/bin/bash
+
+set -exuo pipefail
+
+export VSCODE_OPTIONS=${VSCODE_OPTIONS:-""}
+
+code $VSCODE_OPTIONS $ROOT_DIR