diff --git a/internal/cache/cache_test.go b/internal/cache/cache_test.go
index 3ca28b0..07d619e 100644
--- a/internal/cache/cache_test.go
+++ b/internal/cache/cache_test.go
@@ -3,7 +3,9 @@ package cache_test
 import (
 	"testing"
 
+	"github.com/Masterminds/semver"
 	"github.com/Nightapes/go-semantic-release/internal/cache"
+	"github.com/Nightapes/go-semantic-release/internal/shared"
 	"github.com/stretchr/testify/assert"
 	"io/ioutil"
 	"os"
@@ -39,14 +41,14 @@ func TestWriteAndReadCache(t *testing.T) {
 
 	assert.NoError(t, err)
 
-	content := cache.ReleaseVersion{
-		Last: cache.ReleaseVersionEntry{
+	content := shared.ReleaseVersion{
+		Last: shared.ReleaseVersionEntry{
 			Commit:  "12345",
-			Version: "1.0.0",
+			Version: createVersion("1.0.0"),
 		},
-		Next: cache.ReleaseVersionEntry{
+		Next: shared.ReleaseVersionEntry{
 			Commit:  "12346",
-			Version: "1.1.0",
+			Version: createVersion("1.1.0"),
 		},
 		Branch: "master",
 		Draft:  true,
@@ -59,13 +61,29 @@ func TestWriteAndReadCache(t *testing.T) {
 	result, readError := cache.Read(dir)
 	assert.NoErrorf(t, readError, "Should read file")
 
-	assert.Equal(t, &content, result)
+	assert.EqualValues(t, &content, result)
 
 }
 
 func TestWriteNotFound(t *testing.T) {
 
-	err := cache.Write("notfound/dir", cache.ReleaseVersion{})
+	err := cache.Write("notfound/dir", shared.ReleaseVersion{
+		Last: shared.ReleaseVersionEntry{
+			Commit:  "12345",
+			Version: createVersion("1.0.0"),
+		},
+		Next: shared.ReleaseVersionEntry{
+			Commit:  "12346",
+			Version: createVersion("1.1.0"),
+		},
+		Branch: "master",
+		Draft:  true,
+	})
 	assert.Errorf(t, err, "Write non exsiting file")
 
 }
+
+func createVersion(version string) *semver.Version {
+	ver, _ := semver.NewVersion(version)
+	return ver
+}
diff --git a/internal/calculator/calculator_test.go b/internal/calculator/calculator_test.go
new file mode 100644
index 0000000..5c8f2b4
--- /dev/null
+++ b/internal/calculator/calculator_test.go
@@ -0,0 +1,219 @@
+package calculator_test
+
+import (
+	"testing"
+
+	"github.com/Masterminds/semver"
+	"github.com/Nightapes/go-semantic-release/internal/analyzer"
+	"github.com/Nightapes/go-semantic-release/internal/calculator"
+	"github.com/stretchr/testify/assert"
+)
+
+func createVersion(version string) *semver.Version {
+	ver, _ := semver.NewVersion(version)
+	return ver
+}
+
+func TestCalculator_IncPrerelease(t *testing.T) {
+
+	testConfigs := []struct {
+		testCase       string
+		preReleaseType string
+		lastVersion    *semver.Version
+		nextVersion    string
+		hasError       bool
+	}{
+		{
+			testCase:       "version without preRelease",
+			preReleaseType: "alpha",
+			lastVersion:    createVersion("1.0.0"),
+			nextVersion:    "1.0.0-alpha.0",
+		},
+		{
+			testCase:       "version with preRelease",
+			preReleaseType: "alpha",
+			lastVersion:    createVersion("1.0.0-alpha.0"),
+			nextVersion:    "1.0.0-alpha.1",
+		},
+		{
+			testCase:       "version with preRelease, change type",
+			preReleaseType: "beta",
+			lastVersion:    createVersion("1.0.0-alpha.0"),
+			nextVersion:    "1.0.0-beta.0",
+		},
+		{
+			testCase:       "version with preRelease but broken",
+			preReleaseType: "alpha",
+			lastVersion:    createVersion("1.0.0-alpha.br0ken"),
+			nextVersion:    "1.0.0-alpha.0",
+		},
+		{
+			testCase:       "version with preRelease but broken 2",
+			preReleaseType: "alpha",
+			lastVersion:    createVersion("1.0.0-alphabr0ken"),
+			nextVersion:    "1.0.0-alpha.0",
+		},
+	}
+
+	c := calculator.New()
+
+	for _, test := range testConfigs {
+		next, err := c.IncPrerelease(test.preReleaseType, test.lastVersion)
+		assert.Equalf(t, test.hasError, err != nil, "Testcase %s should have error: %t -> %s", test.testCase, test.hasError, err)
+		assert.Equal(t, test.nextVersion, next.String())
+	}
+
+}
+
+func TestCalculator_CalculateNewVersion(t *testing.T) {
+
+	testConfigs := []struct {
+		testCase        string
+		releaseType     string
+		lastVersion     *semver.Version
+		nextVersion     string
+		isDraft         bool
+		isFirst         bool
+		analyzedCommits map[analyzer.Release][]analyzer.AnalyzedCommit
+	}{
+		{
+			testCase:    "version with preRelease alpha",
+			releaseType: "alpha",
+			lastVersion: createVersion("1.0.0"),
+			nextVersion: "1.0.0-alpha.0",
+			analyzedCommits: map[analyzer.Release][]analyzer.AnalyzedCommit{
+				"major": []analyzer.AnalyzedCommit{},
+				"minor": []analyzer.AnalyzedCommit{
+					analyzer.AnalyzedCommit{},
+				},
+				"patch": []analyzer.AnalyzedCommit{},
+				"none":  []analyzer.AnalyzedCommit{},
+			},
+			isFirst: false,
+			isDraft: true,
+		},
+		{
+			testCase:    "version with preRelease beta",
+			releaseType: "beta",
+			lastVersion: createVersion("1.0.0"),
+			nextVersion: "1.0.0-beta.0",
+			analyzedCommits: map[analyzer.Release][]analyzer.AnalyzedCommit{
+				"major": []analyzer.AnalyzedCommit{},
+				"minor": []analyzer.AnalyzedCommit{
+					analyzer.AnalyzedCommit{},
+				},
+				"patch": []analyzer.AnalyzedCommit{},
+				"none":  []analyzer.AnalyzedCommit{},
+			},
+			isFirst: false,
+			isDraft: true,
+		},
+		{
+			testCase:    "version without commits",
+			releaseType: "alpha",
+			lastVersion: createVersion("1.0.0"),
+			nextVersion: "1.0.0",
+			analyzedCommits: map[analyzer.Release][]analyzer.AnalyzedCommit{
+				"major": []analyzer.AnalyzedCommit{},
+				"minor": []analyzer.AnalyzedCommit{},
+				"patch": []analyzer.AnalyzedCommit{},
+				"none":  []analyzer.AnalyzedCommit{},
+			},
+			isFirst: false,
+			isDraft: false,
+		},
+		{
+			testCase:    "version with commits and first release",
+			releaseType: "release",
+			lastVersion: createVersion("1.0.0"),
+			nextVersion: "1.0.0",
+			analyzedCommits: map[analyzer.Release][]analyzer.AnalyzedCommit{
+				"major": []analyzer.AnalyzedCommit{analyzer.AnalyzedCommit{}},
+				"minor": []analyzer.AnalyzedCommit{},
+				"patch": []analyzer.AnalyzedCommit{},
+				"none":  []analyzer.AnalyzedCommit{},
+			},
+			isFirst: true,
+			isDraft: false,
+		},
+		{
+			testCase:    "version with commits and rc release",
+			releaseType: "rc",
+			lastVersion: createVersion("1.0.0"),
+			nextVersion: "1.0.0-rc.0",
+			analyzedCommits: map[analyzer.Release][]analyzer.AnalyzedCommit{
+				"major": []analyzer.AnalyzedCommit{analyzer.AnalyzedCommit{}},
+				"minor": []analyzer.AnalyzedCommit{analyzer.AnalyzedCommit{}},
+				"patch": []analyzer.AnalyzedCommit{analyzer.AnalyzedCommit{}},
+				"none":  []analyzer.AnalyzedCommit{},
+			},
+			isFirst: false,
+			isDraft: false,
+		},
+		{
+			testCase:    "version with commits and rc release",
+			releaseType: "rc",
+			lastVersion: createVersion("1.0.0-rc.0"),
+			nextVersion: "1.0.0-rc.1",
+			analyzedCommits: map[analyzer.Release][]analyzer.AnalyzedCommit{
+				"major": []analyzer.AnalyzedCommit{},
+				"minor": []analyzer.AnalyzedCommit{analyzer.AnalyzedCommit{}},
+				"patch": []analyzer.AnalyzedCommit{analyzer.AnalyzedCommit{}},
+				"none":  []analyzer.AnalyzedCommit{},
+			},
+			isFirst: false,
+			isDraft: false,
+		},
+		{
+			testCase:    "version with commits and major release",
+			releaseType: "release",
+			lastVersion: createVersion("1.0.0"),
+			nextVersion: "2.0.0",
+			analyzedCommits: map[analyzer.Release][]analyzer.AnalyzedCommit{
+				"major": []analyzer.AnalyzedCommit{analyzer.AnalyzedCommit{}},
+				"minor": []analyzer.AnalyzedCommit{analyzer.AnalyzedCommit{}},
+				"patch": []analyzer.AnalyzedCommit{analyzer.AnalyzedCommit{}},
+				"none":  []analyzer.AnalyzedCommit{},
+			},
+			isFirst: false,
+			isDraft: false,
+		},
+		{
+			testCase:    "version with commits and minor release",
+			releaseType: "release",
+			lastVersion: createVersion("1.0.0"),
+			nextVersion: "1.1.0",
+			analyzedCommits: map[analyzer.Release][]analyzer.AnalyzedCommit{
+				"major": []analyzer.AnalyzedCommit{},
+				"minor": []analyzer.AnalyzedCommit{analyzer.AnalyzedCommit{}},
+				"patch": []analyzer.AnalyzedCommit{analyzer.AnalyzedCommit{}},
+				"none":  []analyzer.AnalyzedCommit{},
+			},
+			isFirst: false,
+			isDraft: false,
+		},
+		{
+			testCase:    "version with commits and minor patch",
+			releaseType: "release",
+			lastVersion: createVersion("1.0.0"),
+			nextVersion: "1.0.1",
+			analyzedCommits: map[analyzer.Release][]analyzer.AnalyzedCommit{
+				"major": []analyzer.AnalyzedCommit{},
+				"minor": []analyzer.AnalyzedCommit{},
+				"patch": []analyzer.AnalyzedCommit{analyzer.AnalyzedCommit{}},
+				"none":  []analyzer.AnalyzedCommit{},
+			},
+			isFirst: false,
+			isDraft: false,
+		},
+	}
+
+	c := calculator.New()
+
+	for _, test := range testConfigs {
+		next, draft := c.CalculateNewVersion(test.analyzedCommits, test.lastVersion, test.releaseType, test.isFirst)
+		assert.Equalf(t, test.isDraft, draft, "Should have draft %t for testcase %s", test.isDraft, test.testCase)
+		assert.Equalf(t, test.nextVersion, next.String(), "Should have version %s for testcase %s", test.nextVersion, test.testCase)
+	}
+
+}