In package karma-coverage-istanbul-reporter it was possible to add threshold for coverage and emit warning instead of failing tests. Here's config example:

{
  coverageIstanbulReporter: {
    thresholds: {
      emitWarning: true,
      global: {
        statements: 70,
        lines: 70,
        branches: 70,
        functions: 70
      }
    }
  }
}

Since former package is now deprecated I tried migrating to karma-coverage.
In package karma-coverage config is changed to:

{
  coverageReporter: {
    checks: {
      global: {
        statements: 70,
        lines: 70,
        branches: 70,
        functions: 70
      }
    }
  }
}

I can't add emitWarning: true to prevent tests from failing and emit simple warning.