Test cases for email validation for Go based on https://blogs.msdn.microsoft.com/testing123/2009/02/06/email-address-test-cases/

email_test.go

package email

import (
	"testing"
)

func TestIsValidEmail(t *testing.T) {
	testCases := []struct {
		name     string
		email    string
		expected bool
	}{
		//valid email
		{
			"Valid email",
			"[email protected]",
			true,
		},
		{
			"Email contains dot in the address field",
			"[email protected]",
			true,
		}, {
			"Email contains dot with subdomain",
			"[email protected]",
			true,
		},
		{
			"Plus sign is considered valid character",
			"[email protected]",
			true,
		}, {
			"Valid email",
			"[email protected]",
			true,
		},
		{
			"Domain is valid IP address",
			"[email protected]",
			true,
		}, {
			"Square bracket around IP address is considered valid",
			"email@[123.123.123.123]",
			true,
		},
		{
			"Digits in address are valid",
			"[email protected]",
			true,
		},
		{
			"Dash in domain name is valid",
			"[email protected]",
			true,
		}, {
			"Underscore in the address field is valid",
			"[email protected]",
			true,
		},
		{
			".name is valid Top Level Domain name",
			"[email protected]",
			true,
		}, {
			"Dot in Top Level Domain name also considered valid (use co.jp as example here)",
			"[email protected]",
			true,
		},
		{
			"Dash in address field is valid",
			"[email protected]",
			true,
		},
		// invalid email
		{
			"Missing @ sign and domain",
			"plainaddress",
			false,
		},
		{
			"Garbage",
			"#@%^%#$@#$@#.com",
			false,
		}, {
			"Missing username",
			"@domain.com",
			false,
		}, {
			"Encoded html within email is invalid",
			"Joe Smith <[email protected]>",
			false,
		}, {
			"Missing @",
			"email.domain.com	",
			false,
		}, {
			"Two @ sign",
			"email@[email protected]",
			false,
		}, {
			"Leading dot in address is not allowed",
			"[email protected]",
			false,
		}, {
			"Trailing dot in address is not allowed",
			"[email protected]",
			false,
		}, {
			"Multiple dots",
			"[email protected]",
			false,
		}, {
			"Unicode char as address",
			"あいうえお@domain.com",
			false,
		}, {
			"Leading dash in front of domain is invalid",
			"[email protected]",
			false,
		}, {
			"Missing top level domain (.com/.net/.org/etc)",
			"email@domain",
			false,
		}, {
			"Text followed email is not allowed",
			"[email protected] (Joe Smith)",
			false,
		}, {
			"Multiple dot in the domain portion is invalid",
			"[email protected]",
			false,
		},
	}

	for _, testCase := range testCases {
		t.Run(testCase.name, func(t *testing.T) {
			actual := IsValidEmail(testCase.email)
			if !(actual == testCase.expected) {
				t.Fail()
			}
		})
	}
}

This list does not cover all possible email address format specified in RFC5321 and RFC5322. Also, Unicode maybe allowed as specified in RFC6531.
More info: https://www.netmeister.org/blog/email.html