I believe we should remove the copyright.

Please use right case and dot:

/// The implementation of the "Remove-Alias" cmdlet.

@daxian-dbw @HemantMahawar @SteveL-MSFT We need new HelpUri.

Issue opened: #15625

I think we should add ValueFromPipeline too.

Please add dot.

Formatting.
I'd remove such comments at all - VS manipulates blocks very well.

Please remove and use -ErrorAction Stop` explicitly in a cmdlet.

Please use the pattern:

   { ... } | ShouldBeErrorId 'ItemNotFoundException,Microsoft.PowerShell.Commands.GetAliasCommand' 

Use -ErrorAction Stop.

Below too.

Space skipped.
And please use normal case for normal words:
"Remove-Alias should remove a non-readonly alias" {

Below too.

Please remove $ErrorActionPreference - see my comment above.
Please add new line at EOF.

Maybe "The alias name to remove."

The exception is already our PowerShell exception so please remove the try-catch and WriteError.

The same please remove the try-catch.

Please add WriteError(error);
And please add new test for the case.

Please remove the extra line in all file.

I think we should protect themselves and add Get-Alias -Name "foo" | Should BeNullorEmpty before trying to remove.

Do you mean as a separate tests before the "Remove-Alias should throw if alias does not exist" test or just like this:

It "Remove-Alias should throw if alias does not exist"{
        {
            Get-Alias -Name "foo" | Should BeNullorEmpty
            Remove-Alias -Name "foo" -ErrorAction Stop            
        } | ShouldBeErrorId 'ItemNotFoundException,Microsoft.PowerShell.Commands.RemoveAliasCommand'
    }

Yes. Only with -ErrorAction SilentlyContinue
Get-Alias -Name "foo" -ErrorAction SilentlyContinue | Should BeNullorEmpty

I think we should keep a consistency and add -ErrorAction Stop to previous two lines - that will exclude false positives.
Please add this in tests below.

Please add an alias for Remove-Alias at : https://github.com/PowerShell/PowerShell/blob/master/src/System.Management.Automation/engine/InitialSessionState.cs#L4656
I recommend ral so we are consistent with gal,sal and nal

Similarly add an entry here for ral

Please remove $FullCLR.

This should be a string[]. All the Remove* cmdlets that have a Name parameter support having a array for names.

The logic here should be updated to remove multiple aliases when the parameter for Name changes to string[].

Please update the strings so that they use better names than foo and bar.

Add a case for ral

@adityapatwardhan We have a test set for aliases in separate file and shouldn't test aliases here.

Correct. Please add tests here: https://github.com/PowerShell/PowerShell/tree/master/test/powershell/Modules/Microsoft.PowerShell.Utility

There are test files for Get-Alias and Set-Alias over there.

@adityapatwardhan @iSazonov sorry, I saw this conversation just now, I'll move the test with the alias, but I'm not sure I understood where I should put them. Currently I have the test together with the other tests unter https://github.com/PowerShell/PowerShell/tree/master/test/powershell/Modules/Microsoft.PowerShell.Utility in a separate file called "Remove-Alias.Tests.ps1". Should I move the whole file or just the test testing for the ral alias?

@PowershellNinja You are right. Changes in DefaultCommands.Tests.ps1 should have you covered to testing alias. Sorry for the confusion.

@adityapatwardhan absolutely no problem, I just was not sure if I have to put the test elsewhere. I removed it in the recent commit.

one of the things that could happen on dev boxes is that an alias tral could exist which could cause some test failures. Since it doesn't matter, should this be something more unlikely to have a collision (say a generated guid)?

@PowershellNinja Could you please address the request?
Sample:

Describe "Remove-Alias" -Tags "CI" { 
    BeforeAll {
        $testAliasName = (New-Guid).Guid
    }
...

i assume that this is a non-terminating error - should there be a test for that? Something like:

Remove-Alias -Name "tral" -ErrorVariable RemoveAliasError 2>$null
$RemoveAliasError.FullyQualifiedErrorId | ShouldBe "ItemNotFoundException,Microsoft.PowerShell.Commands.RemoveAliasCommand"

We have tons of such "incorrect" tests. I think we should refactor them all in time or after resolving #4781

it might be worth adding some tests with explicit scope probes. Say create an alias in scope 3, then remove it without a scope, it should still be in scope 3, etc. I don't think we have many tests which explicitly loot at testing our scopes, so it would be a welcome change

I see that CodeCov reports internal void RemoveAlias falls under tests. Formally we don't get increasing code coverage with the change.
Although I found up to 34 test files with "scope" word in the repo the SessionStateAliasAPIs.cs code coverage is only 68%. I've view these tests before, some look like tricky so I didn't venture to make improvements. I think we need to open new tracking Issue if we want have better scope tests.