implement a function to find the highest supported version

protocol/version_test.go

@@ -28,4 +28,47 @@ var _ = Describe("Version", func() {
 		Expect(IsSupportedVersion(0)).To(BeFalse())
 		Expect(IsSupportedVersion(SupportedVersions[0])).To(BeTrue())
 	})
+
+	It("has supported versions in sorted order", func() {
+		for i := 0; i < len(SupportedVersions)-1; i++ {
+			Expect(SupportedVersions[i]).To(BeNumerically("<", SupportedVersions[i+1]))
+		}
+	})
+
+	Context("highest supported version", func() {
+		var initialSupportedVersions []VersionNumber
+
+		BeforeEach(func() {
+			initialSupportedVersions = make([]VersionNumber, len(SupportedVersions))
+			copy(initialSupportedVersions, SupportedVersions)
+		})
+
+		AfterEach(func() {
+			SupportedVersions = initialSupportedVersions
+		})
+
+		It("finds the supported version", func() {
+			SupportedVersions = []VersionNumber{1, 2, 3}
+			other := []VersionNumber{3, 4, 5, 6}
+			found, ver := HighestSupportedVersion(other)
+			Expect(found).To(BeTrue())
+			Expect(ver).To(Equal(VersionNumber(3)))
+		})
+
+		It("picks the highest supported version", func() {
+			SupportedVersions = []VersionNumber{1, 2, 3, 6, 7}
+			other := []VersionNumber{3, 6, 1, 8, 2, 10}
+			found, ver := HighestSupportedVersion(other)
+			Expect(found).To(BeTrue())
+			Expect(ver).To(Equal(VersionNumber(6)))
+		})
+
+		It("handles empty inputs", func() {
+			SupportedVersions = []VersionNumber{101, 102}
+			Expect(HighestSupportedVersion([]VersionNumber{})).To(BeFalse())
+			SupportedVersions = []VersionNumber{}
+			Expect(HighestSupportedVersion([]VersionNumber{1, 2})).To(BeFalse())
+			Expect(HighestSupportedVersion([]VersionNumber{})).To(BeFalse())
+		})
+	})
 })